You do what you want, but I would have it clean as clean can be. Just have him shoot some foulers before starting the tests. You are testing ammo, not your rifle. And you aren't going to shoot a match so there is no worry about first shot fliers.
That being said, this is coming from a BR guy (I also have multiple RimX's and have had multiple Vudoo's). I know a lot of NRL/PRS guys have moved to the method you describe, but there isn't a single top level competitor in BR that doesn't clean completely. I only say that to say we require the highest level of precision and this "new" method has not proven itself to provide the level of consistency we require. We do play different games, but in this case it's about testing ammo, not the game.
Just one opinion and I am sure others will disagree.