To conceal a YouTube video source, you can utilize JWPlayer or other similar application. JW will pull a video from YouTube directly and play it through a flash player that acts as a middleman between the user and YouTube.
http://www.jwplayer.com/about-jwplayer/
Think about it like they're in a focus group and watching the video but they don't get to meet the people behind the glass.
For a demonstration, visit http://www.wimp.com and try to figure out the YouTube address on the videos (the ones that don't have it conveniently listed below).