I made a mistake 4 years ago.
I said vampires and zombies couldn’t [long] coexist. Because they’d be competing for the same – dwindling – food source: the living (vs them both being undead).
But I was wrong.
If the universe in which they exist is a mash-up of that of Twilight and iZombie … it could work.
The iZombie universe has zombies that can avoid going “full Romero” by maintaining a steady supply of brains – and it’s not much they need to eat to stay “normal”.
The Twilight universe has vampires that can survive on animal blood (or, one presumes, by hitting-up blood banks).
So if you were to have “brain banks” the way you have “blood banks” – I could see it working.
Now we just need some iZombie-Twilight hybrid vambie/zompire creatures running around.