I think you've come across a slightly unexpected product of the changes to entity IDs, zombie villagers and zombies now have separate IDs (hence separate spawn eggs) so a zombie spawner can't spawn zombie villagers any more :(
I do remember at one point in 1.9/1.10 you could find spawners with a zombie villager in (purely cosmetic). I don't think these exist any more for the same reason though. No more villager spawners, get breeding!!