I'm kind of baffled by the idea of the Hirogen becoming a bigger antagonistic race. I thought things between them and Voyager ended positively in the episode with the holograms?
Well, by their very nature, the Hirogen are not a single uniform society or state. They're thousands of distinct nomadic groups, all presumably operating independently of one another. Making peace with one group of them doesn't mean making peace with all of them. The hope was that the new technology and attitudes would propagate through the civilization as they found that there was a better way, but it seems likely that there would be traditionalists who resisted the change, and perhaps became more militantly devoted to their traditions as a result of the pressure to change.