you could look into the exact URL which is blocked and try to allow only the specific URL rather than allowing youtube.com completely. As an alternative you can look into the referer header to allow embedded videos only on specific websites.
We are using specific list of URLs to allow only specific YT videos.
the basic for all videos are:
*s.ytimg.com/* YT flash player + images
*.youtube.com/crossdomain.xml YT player cloud config
*.youtube.com/videoplayback* Flash Binary Stream for requested video
then you can specify video ID in URL to allow specific video
So the rule action is: If URL matches in list ....
there are also some rulesets in the online ruleset libraly available where you can manage youtube content based on youtube category or youtube uploader.
Perhaps this is useful for you.