There is already an option to replace Vanilla Villager with pixelmon NPC.
1.12.2 - replaceMCVillagers=true
1.16.5 - replace-m-c-villagers: true
I want to suggest another option to be added like:
That way all normally spawned villager should be pixelmon NPC
But, if you have already activated vanilla mobs :
then in conjunction with the proposed feature
zombie villager could be cured with the standard method (potion of weakness/golden apple) to "spawn" vanilla villager into the world and make available core MC features (iron golem spawning/trading)