Although it can be a killer to inexperienced players, it is just amazing in harder dungeons, because:
1. Lots of free exploration tiles to help get your health back up if you don't take on the challenge.
2. The zombies don't scale with dungeon difficulty. If you can boost your attack (or physical resist) high enough you can easily do this without using any extra resources. It's not the money that is really important, its all the extra xp.
Also, it is really easy to beat as an assassin if you are 1 kill from leveling. That way every zombie after the first one is an automatic kill.
I highly recommend, that at a minimum, you make the zombies grant no XP.