I guess zombie pigmen share so many properties with zombies, that there is such thing as their villager counterparts. Don't believe me? Do

/summon PigZombie ~ ~ ~ {IsVillager:1}

, you will get a zombie pigman with a flesh head with no skull. If you're going to have something like this in the game maybe you could either remove it or change their model and add the feature of zombie pigmen infecting villagers. But anyways if you do this command, it will spawn a mutated zombie pigman. It also works with babies, use that same command and add IsBaby:1 to it.

PS: Ignore the second photo I didn't put it there, that is in 1.8 I am in1.7.5