He is nowhere to be found in Primm after the NCR raid on the NCRCF, despite the raid leader and the trooper in his tent stating you should meet with him. Also made the NCR the "new sheriff" of Primm, new Sgt. at the sheriffs office; no Hayes.

Maybe the scripts die if you settle the Sherrif matter before the raid? That's how I did it. I may give it a go the other way around, but I'd have to restart.

This seems to effect all versions of the game: http://www.gamefaqs.com/boards/959559-fallout-new-vegas/56824891

He disappeared after I selected someone else to be the sheriff (robo-sheriff for the win!). Hours later, I got to the NCR Camp Forlorn Hope and he's just standing in the middle of the camp for no reason at all.

Did he give you a reward? Did he have anything to say about the assault on the NCRCF? I'd love to know whether or not I've been going crazy looking for this guy for no reason. I'll be sure to check out that camp in my save, as well.