[Endoperez]

Yes, you can. He might attack the caster instead, and will leave after a battle or two or couple, or gets bored. And I think you might get some other Doom Horror even when you Wish for a spesific one. Slave to Unreason doesn't follow your orders... and makes random units, possibly commanders feeble-minded in the province he's in. Pretty nasty, as he will stay parked in that one province.