It is unlikely that IRS whistleblowers will testify behind closed doors in relation to the Biden impeachment inquiry. If any whistleblowers do testify, it will be in a more open setting, likely with congressional oversight. Democrats in Congress have a vested interest in obtaining all the information they can, and witnesses testifying in a private setting could give the impression of partisan favoritism. Furthermore, witnesses testifying before members of Congress carry a considerable amount of public weight, and behind closed doors testimony would lessen the impact of the testimony.
Additionally, federal law requires that whistleblowing activities be public and transparent. Under the Whistleblower Protection Act (WPA), whistleblowers are required to disclose evidence of misconduct publicly in order to have their claims taken seriously. This could provide a persuasive incentive against testifying behind closed doors, since testimony in a private setting would not necessarily have the same power as if it had been conducted in a public forum. Similarly, Freedom of Information Act (FOIA) requests are generally limited to information already in the public domain– which could make obtaining confidential or unrelated information from IRS whistleblowers more difficult.
Ultimately, any decision to allow IRS whistleblowers to testify behind closed doors will be up to the discretion of congressional leadership. Since private testimony carries numerous risks, it is more likely that the Biden impeachment inquiry will remain in a transparent setting to ensure the credibility of both the witnesses and the process.