[DarkRanger]

Evil clerics and blackguards can dominate undead for a short period of time. As far as summons, I think you're only allowed 1 spell summon of any type, casting another spell unsummons the first.

That is correct. You can have a companion and a familiar in addition to one summoned but you cannot have two summons at once.

Not sure, but aren't animal companions and familiars in the same "slot" for game engine purposes?