Bismillah
as salam alykom
I share your strong feeling Intuition for not covering.
See for example a non Muslim can not be the wali of a Muslim girl even if he was her father, brother...etc. But if we like measure the situation against that u cannt uncover in front of a non Muslim woman, then it is even more likely to apply this on a man. In such case he will be just a non Muslim man regardless of the family situation. And yes we can uncover in front of a father in law, because by virtue of the marriage he becomes a permenant Mahram.