I would assume the duct work gets bonded via the EGC to the dust collector motor and enclosure. This is similar to a duct heater.
Static is a whole 'nother thing, particularly if this is a plastic duct. In some of the woodworking BBs they have discussions about this. The fear is "lightning" in the duct could cause an explosion. I would think simply bonding a metal duct would bleed off the static charge.
I do not know of any article that deals with this unless you can call it "pipe" 250.104(B)
