[Radek]

AFAIK, all classes except oomphaz can equip the armor. On the other hand, all roles can equip the armor. Therefore, oomphazes are out of luck completely but, for example, non-oomphaz warlocks aren't.

That's the advantage of the Dragon Armor. Even if it is "only" Plate Mail +2 and even if it is already 4 times enchanted, it can be equipped by any role. The armor is the best armor for bards, warlocks, rangers and similar classes with problems with a suitable armor.
Well, oomphazes are out of luck no matter what role they are. They have to find an oomphaz specific armor. The best armor available to oomphazes is Oomphaz War Plate +2. Note that oomphazes cannot equip Plate of the Realm, either.

Pixies can equip any armor allowed to their role. They have no restriction as far as their class is concerned. If you want a pixie wrapped in a plate mail then don't hesitate and give the plate mail to the pixie.