Ice tyrants would make excellent casters of any kind, they have 18 in CON, WIS, INT and CHA. One problem I have with Dominate Monster is that it only lasts so long (under 24 hours). With the investment it takes to make one of those monsters a worthwhile addition to the party, I'd prefer it were permanent, or at least last as long as it's supposed to according to RAW - 1 day/level. I'd say having to re-cast domination once every 20 days as opposed to every day would get rid of the tedium. It also looks like the dominated monster gets un-charmed if it's hit by an enemy spell. Funny thing, it seems like the monsters can equip and use all the same items as a regular PC.