It works on the PC version, hes playing that version in those videos 
Yes, but I said "how is beyond me", because the PC version has BOTH Online play AND DLC. It might not work on PS3/X360/Wii because there are no reliable modding right now, but whatever. ^_^
Actually, there is no DLC on PC... -yet-. I personally don't take the game online (I have the 360 for that), so I don't know how it would affect it. Also, GH2-360 has been cracked, it just requires a modded 360... which will get you banned from XBL, so it's not very popular.
Anyway, I am the guy playing in those vids, and I'm glad you guys think they're cool too. The Skin chart is amazing, the solo at the end is a lot of fun to play. I can't wait to get the vid up on Youtube once Overworld is out. As far as Empire goes, I can't guarentee my friend is going to chart that one next. He plans to do another Buckethead chart now, and he wants to do either Empire or Ghost next. I've been personally egging him on to do Empire, but I imagine he'll do them both relatively soon. If he can churn those out as fast as he did Skin, though, we can hope to see them both soon.