Yes, Zombies can eat your living Necro alive, though you can have Skeletons guarding you from becoming zombie fertilizer
. On another note, remember that there are a lot of decent Dark Living Creatures out there that can support a Necro deck, primary Demons that deal fire damage because Burn ignore Resilience. Of course, anything with Bloodthirsty or Vampiric is silly against another Necro, but it is uncommon for two Necro to face each other.