I was thinking of doing some type of contest but not actually having the contest be on YouTube, just using YouTube as an advertisement that the contest exists, but then directing them to an external website (an affiliated blog) for the actual contest. As long as you don't embed the YouTube video on the external site to "run" the contest, you're not violating the rules.
I've seen tons of commercials for contests held off-site, they aren't YouTube contests per se, just an ad for a contest being held elsewhere. This is as legal as McDonald's having a commercial for their annual Monopoly contest.