There are some bizarre articles of shaky canon on interspecies sexual reproduction/romance like with Gnomes and Humans or Humans and Dwarves found on the wikias. Or especially Humans and Elves.
In fact, given how humanoid much of even the non-human races in WoW are like, I don't find it implausible most of them could procreate with each other except for the undead.
What about Pandaren though?