I believe “similarity” is the key.

Latin, Greek, Norse, Egyptian, Babylonian (well european and mediterranean)… should work ok in the same deck, and for some reason I’d bet (it’s a shot in the dark 🙂 ) here that far eastern or mesoamericans pantheons should work ok too provided they are in their own decks. Regarding cultures from the pacific and dreamtime spirits, I believe you”d be even more qualified than me to answer that one iirc. 🙂