Return of Reckoning

I've been mostly scouring shops for full item sets for the different classes on Test Server but for some classes it would be awesome to have alternatives helmets really...

Are there cosmetic helmets in the game that characters like a Warrior Priest or Disciple of Khaine can use?

Not many specifically cosmetic hats. There is the kosar helm from events, but other than that not much. I suggest running some PQs and checking out the helms for the influence rewards. Some of them are pretty cool.