Oh yeah hearsay is not admissible.
Yes it is in some instances. Including things like "self authenticating" documents of which there is a long list. Regardless, Pompeo and Rudy's documents can be considered circumstantial evidence.
TS knows he's wrong so he's ignoring all other evidence than one piece of the inquiry that is unavailable on the internet. He basically has his eyes closed, his fingers in his ears and keeps shouting "SHOW THE SUBPOENA!" in hopes that we will get bored and go away. If we do, his flawless, neverending string of victories will remain uninterrupted. Even if we did find the actual subpoena document, I'm sure he has a plan to weasel his way out of acknowledging he was wrong. That's what he does best.