Re: YouTUbe link as a destination URL and Final URL
Yes, it is possible, but you'll also have to have YouTube be the Display URL, too.
Keep in mind that AdWords has a strict double-serving policy - Two Ads from the same domain cannot appear in the AdWords Paid Search Results for a single query. Therefore, if another advertiser is also trying to drive traffic to YouTube for the same Keyword, only one of your Ads will show.
I can't remember for sure, but I think there may be exceptions for driving traffic to a site like YouTube, but for now I'd assume that only one YouTube Ad can appear in the Paid Search AdWords results.