I don't know but I figure it's gotta be independant because if you look further into youtube there are more vids where he's doing some crazy sh!t with articulation without obstacles
I think he has a hydraluic set-up off a Lull or forklift or something. Everything seems to be manually operated. Looks like 4 separate control handles for for differnt tires. Pretty slick set-up. I wonder how it handles on the highway?