Living Dead definitely needs to be tweaked. It's only a safe bet if you have a White Mage who is understanding what is going on AND they have Benediction ready. You technically have to heal MORE than max hp considering the fight doesn't just stop when you go into the zombie state. Some of my suggestions to buff it:

1. Add a built in Convalescence into the zombie buff.
2. Give the Dark Knight a Souleater buff (life steal), DPS increase and Defense UP while a zombie.
3. Add some type of visual indicator, maybe with a large Doom timer and transformation, to reflect the zombie state. A flashing HP bar would be useful.