HM. Just put all bots in team blue or red and players on free? Should work...
Zombie npcs... AFAIK doable, just make npcs with very high perception etc, and with melee as the only weapon... Hm. But last time I checked (it was long ago though) NPCs with melee selected will only stand in place and beat the air with fists. Hmm... Change the AI so they would walk slowly (or not slowly) towards the player? Or maybe do other moves from time to time.