So I got my status with the Powder Gang to "Hated" through helping the good folks at Goodsprings and by killing some other Powder Gangers in the wasteland, yet when I got to the NCR Correctional Facility I was still able to buy my way in and do some quests for their leader.
Should I be able to do that if they hate me or is there a worse faction rating I would have needed to have?
You can be "Vilified", then they'll shoot on sight (or as soon as you try to initiate dialogue, in my case).
About the only thing that's bothering me about this game is how killing random Grunt Y in the middle of the wasteland is noteworthy enough that I can raid a small encampment and have an entire faction at-large now hostile to me. I feel like there's some [censored] with binoculars following me around and then scurrying off to tattle on me to every faction leader in the Wastes. In quests it's one things, but just on the road? The wasteland's a dangerous place. Sometimes your goons are going to bite the dust. Why you gotta hold such a grudge like that?