Whatever it is, it doesn't sound very, um ... impressive. I mean if it is a song on the album, why don't they just play it right instead of half-ass it and have Scott mumbling stuff in the microphone during it which doesn't go with the song at all. That little guitar hook that Dean is doing sounds like the melody from Deck the Halls, the beginning of the part where it goes "Tis the season to be ...".
I don't think it's Maver.