Are they allowed human blood? IDK cause I get confused from game to game, but if they are ayyyye. I think they can be friends. Kieran went out to try and meet more supernatural creatures years before and they could have met then? Stayed buds throughout.
Demetrius thinks, were or no, that he doesn't need any help from a doctor. Coke and liquor never landed him in hospital before! They probably know each other from around though, especially if any of his cases have landed up there.