Whenever Zombie Villagers spawn, none spawn with any kind of Armor. Whether spawned naturally, or by a Zombie killing a Villager, they never wear armor. This makes them very weak.
Steps to reproduce:
1. Spam a Zombie Spawn Egg in Creative (on hard difficulty).
2. Any Zombie Villagers spawned never wear armor of any sort.
And yes, I know that Zombies never wear armor in Easy, but I always play on Hard.