I don't buy that Ghetsis and N aren't biologically related. It's very clear that Ghetsis is a pathalogical liar who hates and regularly insults N, so of course he wouldn't want to be associated with him genetically, let alone openly admit so to N. But the way I see it, Ghetsis bred a loyal servant and order his men to leave the baby in the Lostlorn forest, where Zoroarks likely live nearby. That way, his child can grow up to be deeply connected with pokemon, which would later help him awaken and tame the legendary dragons.