I don't know anything about the "Watchdog Tactical" model but AFAIK all current Mossberg shotguns sport a painted Aluminum receiver from the factory and in my experience the finish seems to wear pretty quickly on the edges, corners, high spots, etc. with any amount of real use. Heck, I have pulled them new from the box with factory applied scratches and blemishes.
Personally, I don't worry about it too much. My personal Mossbergs (a couple 500s and a 930 SPX) are either field guns or defensive guns for shooting not looking. If it is something that really bothers you, I am sure you can have the gun professionally Cerakoted for a couple hundred dollars and not have to worry about it again.
ETA- Hopefully somebody will come along who knows more about the specific model you are asking about.