Hmm. Are you sure that you setup the Nav file? If you don't know how to do this you need to load up the map in NMRiH - press the ~ key to open Dev Console - type "sv_cheats 1" (0 = false, 1 = true) - then type "nav_generate" - this will generate an updated nav mesh file for your zombies and will auto-restart the map - you then should see zombies spawning in - the only other suggestions would be to make sure that the spawns are at the right proportions (32 units away from walls, floor, and ceiling) and to double check your overlord_zombie_helper and overlord_wave_controller settings. :D

Hope this helps and best of luck with the map!