What you're saying about the Jarill / "scavvers" is exactly what I was thinking about why they haven't conquered or been conquered.

They're impossible to pin down, and their homes can pretty much vanish without a trace. Other than their mining operations for the duration of use, they have nothing they can't run off with at a moment's notice.

They don't bother taking planets, planets are places where you need to dig the useful stuff out of holes in the dirt, and then haul it back up a gravity well. Space is full of places no one else wants where there are asteroids and comets full of all the stuff the Jarill need to make new things for use and trade, rocks and comets that the Jarill are better than anyone else at mining, but without the "messy" planets that draw in all the "mudder" cultures.

They don't need to take stuff from anyone else, there's always someplace else to get stuff. Space is really big and full of places no one else wants to bother with.

And for the "big governments", there's more incentive to interact peacefully with the Jarill than there is to start a war with them. War with the Jarill means they stop trading with you... and they're the masters of the revenge strike, popping in to your system, dropping kinetic strikes on your planets (big rocks going fast), and then going away before you can do anything about it.