I don't think its possible to caputire Rhentar-Ihrno, or any of the major characters like Erica. There resistance is probably maxed out, and I dont think a level 99 character could capture them.
My Exile 3 list consists of
Rahkshasha, Pack Leader, Vahnatai Lord, and Vahnatai Keeper.
The Vahnatai lord is nice because it can use its own soul crystal to summon things like basilisks, and the pack leader is good because it hits like 6 times dealing a massive amount of damage. The rahkshasa is nice because i beleive its immune to magic, and the keeper is just something i havent really replaced. I think i used to use him as an archer since i think hes the disk thrower, not sure...