23) One plot I have in my Living Greyhawk Gazetteer Addendum has the current ruler of Ull, Bruzharag the Misbegotten being conceived as an instrument of vengeance.
Draske, the original Orakhan of Ull, murdered his brother, who he saw as a threat to his power. Big mistake: He earned the eternal hatred of his brother's young bride, who loved her husband passionately. She fled to the mountains, where she found sanctuary with her husband's ogre allies. She noticed the sheer strength and fighting skill of the ogre chief, and a plan came to mind...
Many years later, Draske was slain in mortal combat by Bruzharag, the half-ogre son of Draske's former sister-in-law and the massive ogre chieftain who gave her shelter. Bruzharag then seized the throne and set himself up as the new orakhan, giving his mother a prime seat of power as his chief advisor, even as his father is honored by being the ogre leader to receive his royal favor above and beyond all the other ogres in Ulsprue.
Now, this occurred with an ogre rather than an orc as the father, but you could just as easily substitute a really big, really powerful orc to serve as the father.
24) Another case might be a barbarian tribe who is closely allied with an orc tribe. Together, they've proven victorious time and again against any enemy stupid or unlucky enough to cross them.
The intermingling between races has become something more-each race admires the other's physical strength and fighting prowess, and men from both races are taking brides from the other. The half-orc children that arise from this marriage are frightening warriors in combat, renowned for their physical strength and combining the drive and passion of the humans with the savagery and fierceness of the orcs.
In neither case is there any rape-the parents get together either to further their own power, or simply out of a mutual respect and admiration born of the deeds they've accomplished together.