Yes, Nullius normally removes biters without RSO, without regard for the setting. With RSO, there were biters, so I had to add that line.
Quite possibly there is another way to disable them on the Nullius side that would work better for RSO. I don’t know of other precedents of overhauls that don’t work with biters, so it may be an unusual situation. I initially tried to get the game to hide the enemy setting entirely, but had trouble getting the game to do that.
I would think that RSO should react properly if you set enemy base autoplace to nil but didn't check that one. For some reason autoplace is actually ignored for enemies specifically - must had a reson for that at some point.
Added your config and base removal and it works - released 6.2.8 with it.