I think they're pretty close here. Definitely a good starting point. They hit most of the high notes, and if I got creatures like this, I'd be a pretty happy camper.
I do think they can go farther, but that's probably my cultural anthropology background speaking.

Here's some of my own elaboration on them:
Orc
The core of the orc is its hatred. The orc is not a savage brute simply because they lack technology and are stupid. They have outright
rejected civilized society. They are close kindred to the civilized races, and represent what happens when those creatures succumb to their fury and rage and anger and let it possess them and define them. They don't just dislike dwarves and elves and halflings, they actively want to DESTROY these creatures, tearing them from the face of the planet out of an ancestral bitterness that is strong as steel and old as magic, though put into green flesh that is constantly young and renewed by its fecundity. An orc may understand the concept of peace or friendship, but it holds no value for them. What they want is not necessarily to win, but to see their enemies destroyed. It places much more value on your own screaming death than on its own.
The orcs may have some similarities to the mythic view of the old barbarians, the Norse and the Huns and the like. They are an unstoppable force of violence who cannot be reasoned with and who will repay sympathy with obliteration. They scour villages, cities, and kingdoms from the map, and replace them with more orcs, more creatures born, bred, and taught to live close by hate, to nurture it, to renew it, to enshrine it. Orc hate is a cultural burden, a bitterness that they grow in, educated by shamans, and it even drives some to tear out an eye to show their dedication.
Eye motifs are strong in orc society. The eyes of an orc will tell you of the soul inside the individual. Anger is readily displayed, with heavy brows and jaws. An eye torn out represents strength and survival and toughness, but also an undying fury, an implacable rage, a stare that never relents, always watching and waiting for an opening.
Orc hordes form due to their Chaotic Evil nature and their fecundity. They breed fast, and though rivalries often cleave the tribes in twain, the broiling chaos of the orc tribes is such that once in a while, a powerful orc is born who rises to prominence amongst a great swath of orcs. These bands are forces of nature, plagues like locusts, who sweep down upon even the most well-defended cities with the force of a hurricane composed of anger, axes, and blood, leaving terror, sadness, and fear.
Somewhere deep in ancient history is an explanation for this anger. The orcs tell stories about how various races have cheated, denied, and rejected them. Their anger is the anger of the outcast, the anger of the laughed-at fool turned sour, the fury of a creature tricked or mocked once too often. There is always a twinge of guilt related to the orcish hatred: the sense that, in some way, perhaps the civilized races deserve it. Perhaps it is the unkindness and unfairness inherent in organized society that earns this eternal hatred. Perhaps if there were no kings, there would be no orcs.
In my mind, orcs are closely related to the more brutal giants. They work with ogres, trolls, hill giants, and other big, strong thugs, working in close concert to maximize the destruction they are capable of. They rarely build. They prefer to move, to strike, and to encamp.
Psychologically, orcs should speak to the fear of anger in the audience. An encounter with orcs should have the players saying "Holy crap! Those guys friggin'
hate us!" The tenacity and the strength are emblematic of this fury. It's not vengeance -- there is no goal of equality, and no hope for justice -- it's an unquenchable extermination-prone rage, designed to destroy all that opposes them. The orcs might have a mechanic that make them unquenchable or unbeatable. They are good thematic matches with boars: tenacious. They also work well with fire: strong, all-consuming, and terrifying. The main sound in an Orc encounter is screaming: Screaming orcs, screaming people, screaming steel, just lots and lots of screaming.
Gnoll
The gnolls are casual violence. The main sensation to get across with a gnoll is the sense chaos and evil as things that are fun and easy. Gnolls live a life of leisure, taking what they want, tearing apart those who stand in their way, and not concerning themselves overmuch with the consequences of their actions. They enjoy slaughter, delight in blood, and consume all they want. They are fairly happy and content with their lives by and large, gleeful in their attacks, unafraid of wounds on their own flesh, and completely unconcerned with the demons that might associate with them.
Gnolls are a kind of casual evil that befits a very present-focused kind of creature. They simply care about their own personal enjoyment (which includes eating, hunting, killing, maiming, and destroying), and not one bit about what the consequences of that might be. They are scavengers and thieves, eating the remains of society, and digging up the dead.
They fall into associations with demons and undead almost out of habit. Because they like destruction and slaughter, and because they eat the dying and the wounded, they hang around those creatures and those creatures hang around them. Their worship of demons is more an arrangement of convenience than a dedicated obedience. Demons allow them to kill more things, and, in exchange, they just have to kill more things and let the demons have some? Deal. Easy. Show me the nearest vulnerable piece of flesh, and it's paid for.
Hyenas hold a place in gnoll society much like that of family. Though, gnoll family, so useful only in as much as they enable more death and slaughter, and abused and mistreated otherwise.
Gnolls don't often work into huge hoards like orcs, but they also don't take things so very seriously. They are chaotic and evil, constantly at each others' throats, but they're also not overly concerned with being attacked. Their lives have no value, and neither do the lives of any other creature they live alongside. Someday they'll die and oh well, that happens. They are remarkably casual about the violence around them, including that done to them. Some paladin crusading into a group of gnolls to exterminate them is simply behaving, in the mind of those gnolls, like any other creature would: trying to exterminate something. They don't have much of a concept of the future, of the past, of long-term goals, so they don't understand that the paladin might be fighting for something nobler than their own amusement. To a gnoll, there is little nobler than your own personal amusement (often at the expense of another.
Psychologically, an encounter with gnolls should leave the players saying "Woah. These guys just don't give a FRIG about anything!" They'll jump gleefully into melee only to loose interest in a few turns, or they'll run circles around a person just to confuse them. They may attack and squabble amongst themselves over an unconscious PC, or they may stop to eat in the middle of combat because they're more hungry than bored at the moment. The casual violence is high: they'll murder NPC's in droves simply for amusement. There is no goal or destiny with them (aside from possibly a few getting sacrificed to Yeenoghu as a thanks). They just want to kill, torture, and harass, for the LULZ of it. If they are attacked, even if they are near death, it is more FUN for them than frightening. Fear isn't something they feel. Boredom is. They relieve boredom by killing and maiming and sacrificing. The main sound in a gnoll encounter is their bubbling laughter. There's screams and shouts, but many of them are cut short, replaced by the sound of a gnoll's outright glee at the terror on their victim's faces as they see their own lungs ripped from their chest.