A Zombie's normal attack is neutral, so Evil Druid won't help here. It only helps against the special Undead Elemental Hit, it occurs from time to time, but in my opinion it's not worth it.
There are 3 elements which are negated by ED: Shadow, Poison, and Undead. So every attack with these element modifiers will MISS you.
The strength of two elements will be raised: Fire, by 25%, and Holy, by 50%. Means, every Holy attack does like 150% on you, Fire does 125%.
Advantage: No freeze/stone curse for you. +1 INT.
Disadvantage: Heal/Sanc doesn't work on you (and hurts you in PvP, including ME). Bless does, and it GIVES you the buffs, not the offensive blessing effect (-> Bless halves STR, DEX and INT on Undead monsters, but it does not work on ED armoured people).
Zombie Prisoner has 2 special attacks: Poison and Undead Elemental hit. So these two skills will miss all the time, if you wear ED.
Ancient Mummy has Undead Elemental hit (will miss with ED), and Dark Breath. Whatever it is, if it's Shadow, it will miss too.
That's pretty much all I know about ED. :S
Well, if you are a Healer Class, forget it! If not, yeah, then it could be useful, because you're still be able to take pots or meat.