Wondering the same, how about humans and siths?
As i understands it all sith purebloods are mixture of dark Jedi and Sith, so this should work right?
Sith pureblood, pure blood meaning that they are from a lineage untainted by another species interbreeding. However, you are correct that humans (specifically Dark Jedi exiled long ago) bred with the Sith to form the current generation of mixed breeds. At this point true sith with no tainted lineage are but all died out, but I'm sure there are a few who are still true "pure bloods". Otherwise the quest giver on Korriban to search lineages wouldn't bother or find himself superior, apparently some lines kept their family from breeding with outsiders. That's my interpretation of it.
Twi'leks, in the latest incarnation of canon via Clone Wars had hybrid children with humans, so apparently it is possible. Near human species can have children with humans, like Mirialans and I think Zabrak too.