I don't see the purpose behind the vampires. I would stick with the zombie tribe and move Kalitas to the board.
As for blue, your whole deck costs black mana, why on Earth would you splash blue for
Disallow? I can see
The Scarab God working, it's a late drop, works with zombies, only requires 1 blue mana, but you'll never be able to cast
Disallow early in the game when you need it unless you dilute your mana base with blue mana sources and if you do that you run the risk of being colour screwed in a mostly mono-black deck. Unless you want to include more blue zombies. If not, I would suggest losing the disallows in favour of something like
Countervailing Winds, which works great with cards like
Liliana, Death's Majesty.
Just something to think about.