The design should work fine as long as there are 3 allyteams, the exact number of players shouldn't matter much. Potentially scale zombie spawns by the value of the involved armies, so a 3v3v1 (human human zombie) game doesn't totally drown out zoms.
more than 3 allyteams is probably a no-go because "win your objective, prevent other humans from achieving theirs" is difficult to think about with more than one other human
The design should work fine as long as there are 3 allyteams, the exact number of players shouldn't matter much. Potentially scale zombie spawns by the value of the involved armies, so a 3v3v1 (human human zombie) game doesn't totally drown out zoms.
more than 3 allyteams is probably a no-go because "win your objective, prevent other humans from achieving theirs" is difficult to think about with more than one other human