The Alive mod http://www.armaholic.com/page.php?id=23684 has this very nifity profile system which allows for a fully functional meta game. Basically this means that thousands of units can be on the map simultaneously without reduced performance. These units can engage one another and move and function as they would in the real game. When these units come within a certain distance of a player they are spawned into the game. Basically if the undead mod could be integrated to function with the Alive profiling module nation wide outbreaks could be simulated with limited performance loss.