I don't think that Michael would have been entitled to a disclosure of subsequent witnesses. He wouldn't technically be a target of the investigation. The committee would have to target "Organized Crime Penetration of Interstate Commerce" or some such. It would have to be something plausibly related to defined Congressional powers.

It almost would have to be this way: most Congressional hearings are essentially fact finding missions, they can continue for long periods of time, and a committee often won't know who subsequent witnesses will be until they hear what this witness has to say.