To be honest, that is a bad idea.
Black unicorns, unless a well done, well thought out villain, or possiblya coal worker, tend to be have poor welcome. I would say you should go for a lighter color scheme and call him Hard Rock , Bell Toll, or Lightning Ride. Blackenend sounds too much like a “dark n Edgy” OC, which are rarely done well.
As for the friends with Mane 6, no. Never ever do that unless it’s Pinkie who befriends the flippin’ trees. Vinyl or Octavia, maybe. It depends how you swing the concept. Octavia, from what we’ve seen looks to be a typical canterlot snob, and if you go by fanon, she is, so she probably wouldn’t want anything to do with him.
Vinyl may or may not be the punk rock kinda girl, she is in fanon so lets go by that. She would be more open to such a pony and possibly befriend him, depending on how much of a jerk he is, how high her jerk tolerance is with that particular setting, etc.
Aslo, final word of advice, do not make him some gun toting asshat with a tragic backstory, those are hated on sight cause there are far too many. If you want you can make him an ex-Gaurd member or a soldier, but try to keep him a relatively normal guy. Normal ponies get much better reception than ones that try to be dark and edgy.