The idea of biologically dissimilar races from different worlds, different genetics, completely different exobiological or exobotanical chemical make up copulating and producing offspring is just plain stupid, fantasy, and is the worst part of the Trek stories. Let alone the probable differences in copulatory morphology.
Maybe but Threshold show that humanity is evolving to some kind of lizard that lives in swamps and then there is the HILARIOUS Occampa mating cycle were they can only do it ONCE and only bear ONE child (Caretaker, they were screwed before you guys shown up).
And then there is the Andorian "four genders" that makes the Occampa look sane, they have 4 genders and ... let put this, two males fertilize the egg that one female lays and ANOTHER female carries to ... term? I suppose they actually LAY eggs because otherwise the whole thing is dumber that it looks bit Andorian "females" have BREASTS meaning they are mammals on SOME sense.
Somehow what you just posted sounds logical compared with some of the BS Trek writers had put out, heck at least you have the Mule, Liger and other hybrids that show that yes, it can work ...