You'll meet some dorks who deserted from the NCR led by a chick named Layla. You can either pay them a "toll"...in which case they won't go away....inform them there is a sherrif in town who won't appreciate thier behavior, in which case they leave, or you can mouth off to them in which case they commit suicide by Courier. A couple days after you either send them packing or kill them the casino opens up for business. I tried provoking them then going outside in the hopes they would follow me into the street and get killed by Myers but then they go friendly.

If you've installed a sheriff you should have the option to tell them there is law in this town again. And you should have the option to refuse to pay her as well....that leads to combat. I also had the option of asking if they were deserters, after they confirmed they were you start getting dialogue options to attack them...that may only pop up if the NCR is favorable to you though.