I was actually wondering this too... Part of me thinks it'd be totally ridiculous missed opportunity if they don't do it. But the other part thinks "well, probably no one knows she sings on that song anyway."
I've actually NEVER been to a show when 2 bands somehow team up for a song or two--or a show with a "surprise guest" or anything. I always thought that was really Samuel when it happened. --Especially when it's like a huge act and a super huge surprise guest.
I hope they do some fun stuff like that.