[LDiCesare]

I checked with some research. The only other spells the mage could cast on its own are elemental fortitude and heal, I tested all other available spells and the acolyte still casts resist poison on 1st round.
Now, if you give him gems he may do silly things with them, but that remains unlikely.
So acolytes are very good to lead up to 10 hydras, as you want them to move every turn early on, not pausing to site-search/preach/whatever, to just take on armies. Serpent priests only offer faster bless, which amounts to zilch, for an additional 120 gold + upkeep (about half an hydra!).