In any case you'll need a screen of some sort to keep those mages alive. And you won't have any benefit of a communion in this case, too few mages and too little research done.
If you really want to use them for expansion just for the hell of it, then put them behind some principes and spam mind burn. It's not very competitive though.
Quickened war shamblers are pretty effective.. In dom2 I remember them with 2 attacks, fairly high strength. Fightering them underwater I couldsee losing a tart...
I think war shamblers are a pretty silly thing for atlantis to spend its money on. It should all go on seers and deep kings and basically nothing else.