I just came here to say what chulbert said.
Is Bush trying to commit political suicide? Explicitly announcing that your staffers won't be under oath or on the record does not instill confidence your administration's integrity.*
*If there was any integrity to begin with, or if there remains any left to be squandered is up for debate.
I think it would be suicide to let them. Much like the Drkitten post, the questioning will most likely be vague and intended to make them say anything to parade around later for political reasons. Nothing good ever comes from these for the party being questioned regardless of wrongdoing. Without the questioning, it becomes just another coverup conspiracy.