Why wouldn't Necrom have undead? Dunmer have been using undead as tomb guards for generations.
Can't even believe I'm responding to this nonsense, but, here we go.
There is a difference between:
City A: a normal city, one that is of great religious importance to a people. Like Rome, or Mecca. It has (for the basis of its fantasy setting) undead lurking around in the catacombs, or even wandering the streets, if you so desire. These are ancestral guardians per the religion of the people yadda yadda.
City B: a flying city, one that is populated by non-living inhabitants, who fly through the sky, cursing all living things that pass into their shadow.
Which one of these sounds like it makes sense? Hint: it's not City B.