So, after never finding any Daedric Gauntlets, I decided to spawn some with the player.additem command.
According to every source I've seen, the Daedric Gauntlets' code is 0000C582. So I input the command:

"player.additem 0000C582 1" (not with the quotes, obviously)

Which should add 1 Daedric Gauntlet to my inventory. Indeed, I get the message stating that just such has happened, and my encumberance goes up by a certain amount. However, the gauntlet does not show up in the inventory.
I have tried spawning other items, including other Daedric items -- all other items I've spwned have worked fine so far. I tried disabling all mods and creating a new character, and the same problem occurs there as well.

I don't seem to be the only one who has had this problem with this item specifically -- this thread on Gamefaqs shows someone encountering the exact same problem.

http://www.gamefaqs.com/boards/924363-the-elder-scrolls-iv-oblivion/49540071

Unfortunately no solution was posted (it does seem to be an obscure problem). Any help anyone might have would be very appreciated.

Again, disabling all mods and trying with a new character did nothing, but just in case it'll help:
My copy of Oblivion is a non-Steam version (2-disc GOTY box) with the following installed.

Shivering Isles expansion
DLC: Frostcrag, Orrery
OBSE
First Person Sitting
Bruma Guild Reconstructed
Chargen With Numbers
Cyrodill Transportation Network
Darnified UI
Female Imperial Dragon Cuirass
Illumination Within (within.esp is activated, without.esp is not)
KD Cloth Circlets
Loading Screens Themed Replacer (for both vanilla and SI)
Low Poly Grass for SI
Operation Optimization
Reznod's Mannequins
Subtle Sunshine
The Red Vest (this is a small personal mod I made that adds a retextured copy of the huntsman's vest, shouldn't affect anything)
Update My Statue
Xelus's Sister of Battle Armor