It might make sense to have the monsters repulse each other. By spreading out, they'll end up taking multiple paths around obstacles, coming at you from different directions, so it looks like more intelligent coordinated behavior.
I've used this pattern before in game AI's and it works well. If you combine it with a somewhat random searching incentive the "hive" will spread out and search for the player(s). I also let the "hive" communicate with each other if they find a player they let each other know and then set a new waypoint for that area. When they repulse each other they take different pathways around objects and it looks a feels great to play against.
