...I'm pretty sure they still have Unity reputation, even if they might not use radios. So yes, they'll still kill him.
There isn't any way to significantly improve your rep with Unity except time (it goes down each RL day, in case you didn't know).
You can try to find Unity in a versus battle near Broken Hills and hope they don't kill you before you have a chance to use FA on them, but that will only earn you 1 to 2 rep each time. Other than that, there's really nothing I can think of to raise it more rapidly.