Tested on aTV2 jb on iOS 5.3 works perfect. Not as nice as the native aTV Youtube.app but it is a great alternative for those who don't wish to update to higher aTV iOS versions.
Just so you know, I have ATV2 with latest firmware installed but Youtube is still missing. I believe you need ios7 for updated Youtube channel, which means ATV2 is out of play.
I can confirm it works on aTV2's 100% for sure. Should work on any iOS aTV2/3 that supports PlexConnect jb or not.
Its pretty smart they use a random registration code @ http://www.google.com/device and make the channel think its a google device from what I can tell. Just pop in the code using plexweb under the new YouTubeTV.bundle channel and boom, youtube on lower iOS revisions and aTV2's :)
This is not a native Youtube channel but a channel .bundle you can add to PMS which can be served to PlexConnect.