Well, sex with different species is hardly new in Star Trek. Their first alien EVER, was the result of Human/Vulcan mixing. Then there was Deanna Troi, Kehlar, Belanna Torres, Simon Tarses, and many others whom I can't think of right now.
In fact some other sci-fi, such as Larry Niven's Known Space series, and Babylon 5 have featured races where sexual relations is a formal part of diplomacy, (although Ivonova managed to bluff her way out of it.) I believe in the Larry Niven universe it's called Rishathra.