This is a great addition to any PvE server. Not only do the players have to hunt down the zombies but the zombies will actively hunt the players. My only draw back is as an admin one must be aware of the loading on the server. Too many zombies out there will cause significant lag. But that depends on the CPU and the server connection speeds. Go for broke and see what yours will handle.
I run with 100 zombies running around and it does well.