Should Judge Greer be held in Contempt of Congress?
Before you even get to that, he should have been arrested for violation of 18 USC Section 1505, which makes it a felony punishable by 5 years in prison for harming or threatening a witness to a congressional investigation. If he refused to withdraw his order after his arrest, I would have sent the marshalls in, to prevent the violation of federal law, as the FBI is empowered to do.
After Congress comes back into session, if they want to refer contempt charges to the US attorney under Title 2 of the US code, they are welcome to, but they didn't have to do that if the other US law had been enforced.