If no, i doubt anyone can provide proof unless someone who works there become whistleblower.
Or someone could simply do one easy experiment with sending their coins to wasabi coinjoin and see what happens... if bomb will explode, special forces storm your apartment, and your transaction gets rejected for some reason.
The problem is that if they will / do already blacklist, a very low percentage of inputs will be affected. It's probably not going to be trivial manually forcing an input to be rejected.
That does not mean that user inputs are
not already shared with their blockchain analysis company, though!
The problem is not that your input can get declined; in that case, you take another one and call it a day, sure. And if they don't do it yet at all, even better.
What we don't know is whether they're already sharing UTXOs with external companies before each and every CoinJoin. There has been no confirmation or denial of this information, yet.