Only if those balors can't actually summon stuff. I wouldn't want a balor summoning cave lions that would clog the level, run around it and risk getting acid balled or accidentally shot or whatever.
Some other monsters might be summoned that would be undesirable I think.

(Thread necromancer strikes again)

Pets can turn on you, but PV is forever.

Or at least for one turn.

All class abilities seem to provide something flavorful and permanent to the PC; it would seem to me that this would be out of place as is, a one-time effect. I like the concept though.

Perhaps an ability to summon chaos creatures, with stat + corruption costs that depend on what you summon, but with no control over on WHAT you summon. Let's say you get Chaos Rat/Lizard for 1 corruption and low stat loss, and a balor for, dunno, 5-10 corruptions and heavy stat loss. The costs could be balanced appropriately, and would not be reduced by the other class power concerning corruption.

The lore would be something like "You are now able to summon and command your chaos denizens at will". The reasoning would be that the summoning process is very rough on your body and mind, as you have to connect with ChAoS to do so. Given that ChAoS is, well, chaotic, you can't predict what you'll summon (which goes in flavor with the randomness of the other class powers), however it'll only be chaos creatures.

I don't know. Balors are kind of the pets of ChAoS gOds and not mere knights.

By that logic, a Chaos Knight could never kick the ass of an Elder Chaos God, but then again there's ADOM :P.