If im not mistaken this issue has been raised before, especially with midi controller support, and their was no definitive answer given except that it might appear in the next version (possibly V5). This was right around the time that V4 was released. I was thinking that someone, that needed this immediately, could write a plugin if possible in the interim.

As far as video controllers that are in the market already, I know that vegas supports contour shuttle, spaceshuttle, and commandpost. It might support the USB dial thing but i couldnt think of enough reasons to drop $40 on a really cool dial (except maybe color corection??). Try the commandpost. Do a search on it, see if you like the Joystick, Tbar, 15 programmable buttions, then find one online for $15 plus shipping. Thats what I did.