As you say, per the twitter terms of use they're already allowed to use your tweets in their promo materials if they want. There's no reason they need to force-opt you into their ToS if that's all they want to do.

the problem isn't just that this sounds like it was written by a legal alien, it's that they're claiming rights they don't need. The disney ToS outline all kinds of things that you aren't allowed to do, and it's obviously ridiculous to suggest that you can't include their hashtag in a tweet that violates their ToS.