Only the mother's scores matter. I have bred new races which had essences "forbidden" to them from the first generation.i use CB for dummies so i dont know if that makes it different but i just tried breeding a new minotaur which requires Demonic 4, Feral 4 and sacred is forbidden. the sheep slave is depraved and has Demonic at 2.95 +3, Feral 4 +2 and Sacred at -4 +1. I successfully got a new minotaur so negative value of a forbidden skill counts as it not being there as far as i saw. Not sure if thats CB dummies exclusive or just from CB in general.
Btw is the required essence the combined what both parents have or only one Parent? i know that with the additive setting the child gets the combined score of both but does it also count as having the required score?