Any nutrient before cardio reduces catabolic activity (which in turn reduces fat loss). Cardio on an empty stomach is only recommended when intensity is low. Anything higher and you should consume some sort of nutrients.
I do not know of any research that compares fat loss when intensity is low when either a protein drink is consumed or nothing at all. I don't really see a need to perform that study either. Catabolic activity will always be lower when a protein drink is consumed.