I... honestly don't see the problem with Lily/Salazar. Granted, Salazar is kinda... uh, dead in mainstream time, but then again, so is Lily. Salazar... well, he ISN'T a character within Harry Potter. What I mean by that is that his personality isn't explored. He is pretty much a blank slate that the author can do whatever s/he wants with, an OC with a face from the books. It's no worse then having an original character get paired with someone.
Harry/Vernon... that I have a problem with. Urgle! Talk about tasteless. At least with Draco or Snape you have the excuse of... well, actually, I really can't think of ANY reason why Harry/Snape or Harry/Draco works, but Harry/Vernon is... definitely worse.