Torchbug
Are you talking about the Powder Gangers who attack Goodsprings and live at the correctional facility? I don't think they are a faction you can "join" really (they're not involved in the battle of Hoover Dam or any main story stuff iirc) but you can be on good terms with them if you help them kill the people of Goodsprings, when they attack the town. I think it's also possible to enter their camps while wearing their armor. It's been a long time since I played that game, though, and I never tried to get along with them. I protected Goodsprings from them.