Actually, there is some sort of a connection between the Reavers and the K'hara, which could be compared to the Nomad-Outcast or Nomad-Spectre matchups.
As far as I'm aware all of it is in-game presence, which, there's nothing wrong with that. The Nomads, just like every other human being that's not shot on sight by them, see them as a tool powerful enough to use, a tool that wants to be used as well.