Did you know that? (Dominions trivia)

[Renojustin]

I think stealthy units attack in the magic phase when there is an additional friendly ritual cast on that province, like a remote summon. So they will fight with your summons.

AND/OR stealthy units attack in the battle phase when you have an army moving in, to combine forces with the army.

I THINK. Not too sure what would happen if you ritualed a province then attacked it... but then that's not such a terrific idea either, most of the time.