As long as the beliefs do not get in the way of the relationship, I would certainly date a theist. I think we could still hold a sensible and healthy relationship as long as the subject of religion is not raised.
Christianity: The belief that a cosmic Jewish Zombie who was his own father can make you live forever if you symbolically eat his flesh and telepathically tell him you accept him as your master, so he can remove an evil force from your soul that is present in humanity because a rib-woman was convinced by a talking snake to eat from a magical tree...