What, this thread isn't about the merits of getting your Psychic ally to join you in your war, thus giving him the opportunity to use his Allegiance Subverters against your enemy's ships, gaining them for himself???
(I used to do something similar all the time in MOO2 - someone would ask me to declare war on someone, I'd do it and conquer all my new enemy's planets and my ally didn't even mind that I had expanded so!
)