Can pagan holy orders be used against other pagans?

In my current game I am the king of Sweden and have reformed the Norse faith. I have access to the Jomsvikings holy order and have raised them to help out in a holy war against a Slavic duchy. However, in either sieges or battles the holy order does not fight, in the same way as if I was attacking a member of my own religion. Is this intentional? Which religions will Norse (or other pagan) holy orders fight against, or under what conditions will they fight generally?