I just watched the video and I don't think it will cause any problems as long as you don't get too crazy with the drill. If you use a fine steel wool, plenty of lubrication, and keep the drill on a medium speed while constantly passing back and forth through the barrel to prevent it from getting warm in certain areas, I think that procedure would work, especially if a barrel is as fouled as the one the guy showed in the video.
I like to clean my gun regularly to keep things like that from happening, though. But there are certain situations where a gun can get absolutely filthy. I cleaned a few old shotguns for my grandfather a few weeks ago that were extremely dirty. I honestly don't know if they had ever been cleaned before. I just used a wire brush, Hoppe's #9 and a little elbow greece and cleaned the bore up pretty nice. I don't know if I would ever use the procedure the guy posted in his video, but again, I don't think it would cause any serious problems as long as you're careful.