Notwithstanding all of your humble "I have no idea" assertions, nimh, you've convinced me that you're some kind of bottom-feeder. That's seems like a pretty exhaustive legal analysis that requires a fair amount of research and perspicacity.
I suspect Trump's main question will simply be "Yeah, well, what are ya gunna do about it, cowboy?"
For what it's worth, Trump himself is refusing to take a salary. And he could obviously afford to pay a good salary to anyone he wanted to do anything he wanted. Not that his son-in-law needs any salary, either, of course.
I would guess that most courts would find that these "anti-nepotism" laws are designed to keep relatives off of the public tit. Beyond that, who really cares?