"Crazy good": Yes. I'm not a fan, but he is a monster slide player.
I don't have the DVD, but this
makes it look like he's muting with the heel/little finger of the picking hand. He's also playing with a pick, which takes away the possibility of muting with unused picking fingers. For maximum freedom on slide I recommend fingerpicking w/slide on pinky, an approach that leaves the most digits free to do more stuff as you grow as a player.
"You can't write a chord ugly enough to say what you want to say sometimes, so you have to rely on a giraffe filled with whipped cream." - Frank Zappa