Mossberg may not be a "Pro-Staffer" or "Barrel Sticker" gun, but they do work. Just ask the Marine Corp and the U.S. Skeet team. They are not glamorous and don't begin with the letter "B", but they do work. In the non-too distant past, all you could find in the duck blinds were Remington, Browning, and Mossberg.
Duck Commander is going to endorse whatever sponsor that will support him. I don't believe that he has a product loyalty to any brand.