I kept a holstaurus in my house and added a nametag to ensure that it didn't de-spawn (just to make sure) and it got bitten into a zombie villager. After reviving the standard way using a potion of weakness and a golden apple it revived into a normal villager instead of a holstaurus. I can confirm it is the same entity as they have the same nametag and it is a solo world.

The Holstaurus and the passive/villager-like mobs in the mod are based on the vanilla villager.
Anything that effects the villager also affects the mobs based on them. This includes zombification and villager habits.