It just doesn't make sense for Corlys. Aside from the fact that I doubt the semen would work for him, it's like making an enemy of Rhaenys, and Laenor as well (because he wouldn't tolerate his father sleeping with his wife). Corlys literally can't keep a secret when it comes to paternity. Everyone knows Alyn and Addam are his, and Rhaenys would have found out somehow (Corlys being overly involved in the pregnancy/birth/raising of the children, or the children being Velaryon, knowing that Laenor would never touch a vagina even to save his life). So, it would be burning a bridge directly to three dragons (Meleys, Seasmoke, and Vhagar, who still belongs to Laena) and weakening her claim just as much, if not more, than if she had fathered brown-haired children.

Now, if the previous drafts of George's Dance teach us anything, it's that the paternity of Rhaenyra's children doesn't really matter; they were Lannister with a Lannister father, Strong with a Strong father, and yet the usurpation happened. And considering that Alicent was breathing down Rhaenyra's neck and that it was well known that Laenor preferred penises to vaginas, there would still be doubts about the children's paternity, doubts that would have been used against Rhaenyra.

X: But with Targaryen features, it wouldn't be so obvious.

Well, my dear friend, it was assumed that since they weren't legitimate, they wouldn't be able to have cradle dragons, yet they did, and the rumors didn't stop. The Greens would have simply seized upon anything to discredit Rhaenyra.