I think Dom won't be able to resist occasional trolling because he's that kind of guy, but he'll lay off and not give him the worst. Definitely friends!
I think he'd be friendly with Diego too. I really doubt that all of the prefects would be anti parties, lol! As long as the thrower didn't do something stupid to get them all caught, or hurt, Dominic is probably pretty relaxed.
I think Dom has learned not to jump in every time Sy starts verbal sparring, but if whoever he's with looks genuinely upset or there's something else going on, he'd try and get him to step off. And yay wingmen ;)