Is "Duck" just a cute brand name for duct tape, or is it a reference to duck cloth? (a type of heavy canvas)
Cloth tape should be fine for ductwork, but it's not because they use the wrong adhesive. I would go to an HVAC supply store and buy whatever they recommend for ducts. Cloth or aluminum should work equally well. If you go to Home Depot or Lowes to get your tape, buy the aluminum tape.