In a regular trial, both sides (prosecution and defense) generally have an obligation to inform the other of any evidence (including witnesses) they plan to present at a trial, and to allow the other side to examine the witnesses or evidence before the trial starts. That process is called "discovery." It's not unusual for one side or the other to spring a "surprise" or "last minute" witness at a trial, but they have to justify the lack of notification to the judge. If they can't justify it, the judge can either refuse to let the witness testify, or declare a mistrial.
No such rules apply to a Senate hearing, because it isn't a trial. Besides, the Senate committee did notify Tom in (somewhat) advance, because, as we saw, Tom's "you've opened yourself up to five counts of perjury" speech occurred several days before Frankie took the stand.
Correct on all counts.
As an aside, even if this were a jury trial, Frankie could be called as a witness against Michael without notifying the defense because he would be a rebuttal witness, whose testimony is merely offered to impeach the veracity of the Defendant's (or any witness' for that matter) testimony. Because the testimony is not part of the Prosecution's case-in-chief, there is no obligation to reveal this witness to the defense.
It's one of the many reasons why a criminal defendant should consider not taking the stand.
