Fiorello's page

Lokie wrote:

And technically... the monk is still not proficient with it as I quoted from the PRD. If you look at what weapons and armor the monk is proficient with you'll see that "simple weapons" is not included and neither are unarmed attacks or gauntlets. His class feature that gives him improved unarmed strike is technically the only reason he can punch, knee, elbow strike, or kick at all. :)

PRD on weapons:

Pathfinder Core Rulebook p.141: Equipment -> Weapons -> Simple, Martial and Exotic Weapons wrote:

... All characters are proficient with unarmed strikes and any natural weapons possessed by their race. ...

But I'll happily agree that monks are not proficient with gauntlets.

But aside from the damage being lethal a gauntlet counts as an unarmed strike in all ways. Therefore every class is proficient with them.