That is fantastic! The whole concept of "maintaining a visual theme" is something a lot of publishers don't give enough weight to, the one thing that really stands out to me from big publishers like WotC, Fantasy Flight, and Paizo isn't so much the quality of their art but rather the commitment to having a consistent aesthetic style. But smaller publishers can do the same thing, games like Symbaroum, Numenara, and The One Ring all have this consistency that speaks towards a real care for for the property.
One of my most recent disappointments was the third edition of Exalted, the book has a great deal of art and even funded extra art with stretch goals, but more art doesn't necessarily mean more GOOD or APPROPRIATE art. They really lost out on the opportunity of setting up a real aesthetic for the game line going forward in this new edition. Far to much of the art was either vague and generic, detached from the flavour of the text, or in odd 3D poser art or cartoonish styles that stuck out like a sore thumb in contrast to the rest of the book. This was actually a step backwards from the previous edition core book, whose art may have been more modest overall, but struck a much more definitive aesthetic.
If you can afford the
Lord of the Ring license or have
half a million dollars to do it, it's a crying shame not to see a strong art theme in your RPG book. If I can get the sort of funding Symbaroum got, there will
definitely be totally killer artwork throughout all of
Mists of Akuma!
The whole model of tabletop publishing has transformed considerably over the past decade and while the industry has become
far more accessible (which is a good thing) thanks to the internet (read: publishing tools, resources marketplaces
(stock art, page templates, etc.), and crowdfunding), it also ends up sending production values way topsy-turvy. Before a publisher looking for artwork to put in a book pretty much had to have some serious capital around to pay for that right out -- now they can go to a website and drop a fraction of that to get (sometimes very good) stock illustrations. That cuts down production costs but it also cuts down prices; when prices get hit across the board, that comes back around to knock down capital for projects.
I think that's why you're seeing those sorts of things happen, though I didn't even get that far with Exalted (
recent doings on their part put them right out of my reading bin -- I wouldn't be surprised if somebody in their art department decided to look for greener pastures around then).
Morrus and Green Ronin use art studios (collections of artists that band together as opposed to a team of freelancers) and that definitely works like a charm -- but they had considerable capital to do that. If you don't have the funds to budget original artwork for an
entire book, you're in a rough spot indeed!
In
Veranthea Codex we had different artists for different continents and the library of stock art available to RGG was enormous, but the whole concept there was a radical mixup of settings (and
reports so far are that we nailed it 
) so having varied themes wasn't an issue.
Hypercorps 2099 has visual themes reinforced with each chapter's opening (full page illustrations by the single major interior artist, a great guy named Nathanael Batchelor), but getting cogent stock art to fill in gaps where I needed it was pretty easy to do because I was shooting for a comic book feel.
That said, I
really want to have a strong, consistent theme to the artwork in
Mists of Akuma.
We did a two hour discussion and blind art corral between the designers to figure out which of the applying artists were up to snuff, and in the commission e-mails I made it clear to all the prospective illustrators that they'll be working to emulate a Lead Artist
specifically so I can get a solid visual theme throughout the final book.
The cover artist is confirmed though and I know he'll knock it out of the park and set the stage just right (I'll let Morrus reveal who that is

).