That was only half my point. Only humans and powerful magic monsters historically have been able to crossbreed with other creatures.
Oh, you're no fun anymore.
D&D is filled with examples of odd crossbreeds. IN 1e, orcs can breed with humans, goblins, and hobgoblins, for a start. In 3e look at the examples of the half-fey centaur, half-troll, and so on.
If you count ecology articles, night hags breed with humans or elves, their greenhag offspring breed with ogres or hill giants, and the annis is less discriminate.
I went so far as to have a tribe of half-troll ogres and half-ogre trolls living together, but then again I also devised the Median Mixture; a potion that enabled two imbibers of differing species to become viable with one another.
One PC in my game is an oceanid, offspring of a salt hag and triton. Salt hags, in turn, are the offspring of night hags and sea elves. So yeah, I throw typical genetics right out the window - it's a game, after all.
As for the half-orc/half-dwarf, if the dwarf was a PC, then it is their choice, of course. Problem solved. Should they choose to keep the child, I can see numerous plot emerging.
Perhaps the dwarven woman seeks council with a tribal elder, who interprets omens and portents to determine that the child will be a powerful asset. The child is born as a sorcerer or warlock.
Perhaps the dwarven woman chooses to have the child but does not wish to raise it. She travels to a nearby temple and learns of an orphanage. There she discovers numerous kobold, goblins, and orc children, all orphans after "heroic" adventurers slaughtered their parents.
Perhaps she chooses to terminate the pregnancy, using the aforementioned herbal remedies, only to discover that the ghost of the infant now haunts her dreams. Alternately, the child is reincarnated shortly thereafter - as an orc.
Perhaps the orc wasn't an orc at all. He could have been a doppleganger or the victim of a polymorph spell. But then again I have too much fun, for people.
