[Taqwus]

I don't know if immortals have a lower chance of getting afflictions, but at least in Dom I, they do heal them over time. Pretenders also have a chance to heal afflictions when resurrected by their priests.

But generally Gift of Health would be the way to go. Within your dominion, you get bonus hit points AND can heal afflictions; very nice if you've got robust troops like Jotuns.

And yeah, if you want an Arco priestess but aren't playing Arco, you either need to charm one (there's multiple charming spells, or at least their were *shrug*), or wish for one (probably not the best use of a wish...).