It would be more viable for species with similar physiologies to interbreed with each other, such as Trandoshan/Barabel or Geonosian/Verpine or Chiss/Human. It is more down to genetic compatibility in a realistic sense as to whether species are capable off producing cross-bred offspring.
However, one could imagine that desperate parents might get something done artificially if their species aren't compatible for standard means of procreation. That's how Hutts and Jawas make babies. Perhaps an explanation for all those sentients running around claiming to be the result of illogical breeding between two very different species.
Just my opinion on the matter. As for official sources, don't know any I'm afraid.