Maybe it's the level of control one has over the other that's the key - there's gotta be some conflict, with 2 individual consciousnesses living together like that - I'll sleep on it.
I doubt we can prove anything either way, Dax is written as a mystery. I think it's an interesting concept and worth thinking about. A little.
If I already had a cogent view on this topic, I wouldn't have been itching for the discussion. I'm still leaning towards the "Dax is a heartless asshole' side of it.