Here's what I mean, and what I thought you were also referring to, but in a different way. The tournament would have been wise to ensure that all the players going into the draw had presented proofs that they are eligible to enter the country. Because if they can't enter the country, they can't play, right?
But what I took you to be saying was that the tournament should single Novak out and demand that he answer the question, before the draw is made - based upon the obvious likelihood that he's unvaccinated. My feeling on this is that it would be unfair to single him out in this way. That they either ask everyone, or no-one.
Now, this is not a contradiction of my view that there maybe back channel stuff going on. If there is, it would by nature be informal. But to formally insist he presents his bona fides while not asking the same of others would be unfair. He may not even answer, and they have no ruling in place that they can force on him.
I do understand the distinctions between the treatment of foreign citizens and Americans with regards to the vaccine, and also I understand that the USO have no say in government policy...