I would have thought if a hummus had feta or Parmesan in it would say (or at least hint) in the description. IMO not "normal" hummus, but specialty/flavoured hummus. Sometimes Moroccan ones have honey in though, I've never seen ones with feta or Parmesan in a shop/restaurant.
It it's just plain hummus, I wouldn't worry. If it sounds like it has lots of other flavours/etc in there, may be worth asking, depending on the flavours. I.e. "herby" sounds fine, "morroccan" or "pesto" and I'd ask.