Star Wars RolePlay

I don't see why not, but if you wanted to use anything about the species that isn't currently canon (not a lot) then you'd need to write a species profile for them.

Gotcha. The only reason I ask is because I see Sith Pureblood aren't playable so I thought maybe it is the same deal with Massassi?

The Massassi are on the Approved Species List