I just did the same thing. The thing is I was told by the colonel to kill them. That, and they helped get me shot in the head, and they are drug dealers, etc. So I just got a scope for my hunting rifles and used their heads for target practice.
Odd thing is, other than the first ghost town I visited going to their place, they were not hostile. I just sat up on a ridge and popped them off. I went into the room with the leaders and just threw a plasma grenade at the feet of the guys at the end of the room. Cass and her Riot gun took care of the rest (love that girl).
So I never really saw that talking to them and making any kind of deal was an option. Just like with the Brotherhood. The colonel basically said outright to just kill them. So I did. House I wanted to talk to about it but again no real option to do so. I even left him alive and the Colonel had some of her men go to the Lucky 38 and 'finish the job', and then I see Mr. Houses obituary on the pipboy. Overall the NCR just doesn't want anyone else around.