Short RAW answers: no and no.
A magic item's magical properties begin and end with the effects described in their writeup, plus some general properties that all magical items have; otherwise, they behave like normal objects of their type. So beyond increasing the user's Strength, the Gauntlets of Ogre Power behave like regular gauntlets.
Punching someone while wearing gauntlets is treated like any unarmed attack: all characters are proficient in it, and it does 1 + Strength modifier damage (granted, the Gauntlets help a lot on that Strength bonus part).
Note that there isn't anything that specifically says a gauntleted punch isn't any different from an unarmed attack, but since there isn't anything that says it is, you go with the more general rule.
A DM may want to rule instead that the gauntleted punch is an improvised weapon instead of an unarmed attack, so it'd be 1d4 + Str for the damage (technically, you'd do that if you picked up a gauntlet and slapped someone with it), but even then, the Gauntlets of Ogre Power aren't weapons, so they can't be magical weapons.
The comparison here is like what would happen if you picked up some other non-weapon item and smacked someone with it (except staves, which specifically state that they can be used as a quarterstaff). Whacking someone with a Belt of Dwarvenkind is certainly a fun image, but it isn't a weapon.
Rule of Cool Answer: DM's call, but be consistent
The idea of a desperate hero picking up a totally inappropriate magical item because they're up against a monster with immunity is kind of fun, so a DM may well rule the exact opposite of what I said above. It's not like choosing to use the Gauntlets of Ogre Power is going to be an unbalancingly powerful option, since literally any other weapon in their hands would do at least as much if not more damage.