When you're the defense in a court based situation - whether it's criminal or not... Yes, you can subpoena whomever, you can present evidence, and in doing so... Potentially reveal other misconduct with your testimony.
For example: in his speech, he specifically mentioned to keep things peaceful, his tweet that went out before he was suspended...calling for peaceful protest... When contrasted against for example- Ray Epps. Ray Epps was caught on camera many times directing unpeaceful protest. The public was able to connect Ray Epps to FBI pretty quickly, imagine how easily it will be to do that in court.
Basically - the only thing that comes from this entire thing is the DOJ, FBI, and Jan 6th Committee spelling out how they are actually the insurrection specialists.