I made a set of gauntlets and of course there are .mdl files for them, but they do not appear on my character when they are equipped. do gauntlets ever appear? if not...then why are there .mdl files for them?

Gauntlets Don't Appear In-game As Such You Just Equip THem And Get The Bonuses...

most likely the models you are referring to are artifacts from nwn and were not fully removed as there might have been plans to implement them in the game. However as was mentioned they are not actually used in game. In order to give a character a special set of gauntlets as an appearance you would have to edit the main body model itself.