In my Evil playthrough, I decided that I would help the Powder Gangers take over Goodsprings, but 30 seconds into my conversation with Joe Cobb, I couldn't resist stepping back and throwing a spear into his face, and then blowing up all of his compatriots in Vault 19, Primm, and the NCR Correctional Facility. I mean, it can be fun to play as the bad guy, but the Powder Gangers are just so... pathetic. They're a bunch of cowards and bullies and it grinds my teeth to even consider joining them. At least the Legion's leaders enjoy a good fight, even if they go about slaughtering/enslaving the weak and infirm afterward.
So yeah, did anyone join up with them? I don't have it in me to try.