It depends if they computer players need to be on a players team or not. It is possible to make creeps attack each other (Neutral Passive Vs Neutral Hostile Vs Neutral Victim) as I have done it. However, I eventually abandoned the system (as it got very complicated) and I decided just to use player 11 and player 12. Basically the way I had it set up, was at the start of the game, I created 2 player groups and added Neutral Hostile and his allies to Player group one and Neutral Passive and his allies to Player group two. Then I set it so that all players of player group 1 treated other members of the same group as allies. And all players in player group two treated members of their group as allies. Finally, I wrote another trigger, declaring that every player in Player group one treat every player in Player group two as enemies. (It got a little complicated when it came to forcing units to attack other units, and it also had a few glitches with item drops and bounty,(Which might be correctable))
Hope this helps!
