It's not really a non-faction, it's based on the existing factions, and the assumption that the galaxy isn't just made up of the 50 planets within a GC.
I appreciate the logic though it would seem to make more sense in a perfect world if they raided my undefended cash cow planets at the rear of my respective empire rather than hyperspacing into an enormous cluster of ISD IIs - however I imagine there are more than a few limitations with the EaW engine in this respect.
Either way it hasn't effected my enjoyment of this excellent mod!