May be a bit more complicated than that. If the rumours are to be believed, some of the evidence may directly point to UCI being involved in covering up positive dope tests. In those circumstances they would notionally be judge and co-defendant. It puts USADA in a dilemma. I'm sure they will follow the rules to the letter, but putting it in the public domain at the same time as UCI gets it would go some way stymying any attempt by them to suppress or distort the report.
The publication of the evidence will set in train events with consequences for Armstrong and his backers, for the UCI and their relationships with WADA and the IOC and for the wider cycling community. It's going to be messy and long. We've only got red light and cunobelin to deal with, they're going to have every cycling wide boy and their lawyers baying foul.