The gauntlet is being treated as a "weapon", so you can use it, OR you can use your unarmed combat skills.
That's a weird magic item, one that has arcane spell failure. Homebrew, I imagine. Theoretically, spell failure stacks, so the guy would get 20% spell failure.
A monk can use a gauntlet, just takes -4 nonproficiency unless he's proficient, and only does D3 damage, no matter what his unarmed damage is.
So no, they're no good for unarmed combat.
Monks exhibit proficiency with both "Gauntlets" and the "Strike, Unarmed" weapons in Pathfinder, despite the absence of explicit mentions in the weapon proficiency list. To challenge this would imply that monks are not proficient with the "Strike, Unarmed" weapon either because they are also not listed. If one argues that proficiency requires feats such as "Simple Weapon Proficiency (Weapon: Gauntlet)," consistency would demand the addition of a corresponding "Simple Weapon Proficiency (Weapon: Strike, Unarmed)" feat. Failure to acquire such feats would result in a -4 penalty on attack rolls for "Unarmed Strikes." Notably, the "Improved Unarmed Strike (Combat)" feat, while enhancing unarmed strikes, does not confer proficiency with the specific weapon "Strike, Unarmed."
Monks are proficient with the weapons “Gauntlets” and “Strike, Unarmed” even though it doesn’t say they are proficient with ether in the weapon proficiency list. If you do not agree with that then technically, a monk isn’t proficient with “Strike, Unarmed” weapon either. If you say they have to get a feat like “Simple Weapon Proficiency (Gauntlet)” then they would also have to get the feat “Simple Weapon Proficiency (Strike, Unarmed)” or they would be taking –4 penalty on attack rolls even for a “Unarmed Strike.” Because the feat “Improved Unarmed Strike (Combat)” doesn’t also give them proficiency with the weapon “Strike, Unarmed”.
Pathfinder: Core Rulebook: Page 57
Monk “
Weapon and Armor Proficiency: Monks are proficient
with the club, crossbow (light or heavy), dagger, handaxe,
javelin, kama, nunchaku, quarterstaff, sai, shortspear,
short sword, shuriken, siangham, sling, and spear.
Monks are not proficient with any armor or shields.
When wearing armor, using a shield, or carrying a
medium or heavy load, a monk loses his AC bonus, as well
as his fast movement and flurry of blows abilities.”
Pathfinder: Core Rulebook: Page 146
“
Gauntlet: This metal glove lets you deal lethal damage
rather than nonlethal damage with unarmed strikes. A
strike with a gauntlet is otherwise considered an unarmed
attack. The cost and weight given are for a single gauntlet.
Medium and heavy armors (except breastplate) come with
gauntlets. Your opponent cannot use a disarm action to
disarm you of gauntlets. ”
Pathfinder: Core Rulebook: Page 149
“
Strike, Unarmed: A Medium character deals 1d3 points
of nonlethal damage with an unarmed strike. A Small
character deals 1d2 points of nonlethal damage. A monk
or any character with the Improved Unarmed Strike feat
can deal lethal or nonlethal damage with unarmed strikes,
at his discretion. The damage from an unarmed strike is
considered weapon damage for the purposes of effects that
give you a bonus on weapon damage rolls.
An unarmed strike is always considered a light weapon.
Therefore, you can use the Weapon Finesse feat to apply
your Dexterity modifier instead of your Strength modifier
to attack rolls with an unarmed strike.”