Do zombie villagers in the Xbox 360 edition spawn randomly or does there have to be villagers in the world originally
As of TU14, Zombie Villagers are part of console edition.
Zombie villagers comprise 5% of all spawned zombies. They behave as ordinary zombies, but their character model's head and face is reminiscent of that of a villager, shaded with a darker green hue.
Zombie villagers can also result from zombie attacks on villagers. If any type of zombie kills a villager, there is a chance that the villager will transform into a zombie villager (100% on hard difficulty, 50% on normal, 0% on easy).
Zombie villagers will spawn in worlds where there are no villagers.
A few months ago, Zombie Testificates were added in an update to the XBox 360 (I don't have it for PC, so I was super psyched when I first saw this).