Of course, the problem will still be that if they issue a subpoena for the whistleblower and he refuses to show (or any other hostile witness), presumably there won’t be any recourse apart from enforcement action based on a committee vote, which we know will fail. Same for any questions Schiff refuses to answer if he goes under oath.
The rule is a real thing, but the site that claimed Nunes invoked it (including a letter) has been scrubbed off the internet.
-PJ