first of all set independants friendly to nobody, this makes the zombies attack all military factions. to make them attack civvies, spawn a soldier and look for the 'probability of presence' slider, turn that all the way down. That makes the soldier never spawn. Now use the group tool on the civilians and link them to the soldier, make sure the soldier is set as their group leader. This now marks the civilians as a military faction and they still won't act any differently.

There's probably a much better way but that's how i've been doing it since arma 2.

The only problem is I'm attempting to do this in a zeus game, and I don't think there's a probability of Presence slider in Zeus. But linking it so a person from a military faction is there leader is still genius. I'll try that out