The guy's name is Justin Bihag -- AKA Justin Chapman, who's been referred to as Dog's nephew on TV -- and he got paid a visit by cops on Sunday down in Edgewater, CO ... where police say he was in violation of a court order to lay off booze and drugs.

How this exactly came about ... Dog's own flesh and blood Lyssa, his daughter, tipped the local police off to Justin's alleged bad behavior -- this according to the arrest report, obtained by TMZ.

The cops checked it out, and sure enough ... Justin was on probation, so they went to his place to see what was up. The responding officer says the guy reeked of alcohol and there were signs of marijuana in the house too. During the convo, Dog himself got roped in.

The cops say Justin called Duane on the phone, who apparently tried calming him down. The chat didn't get him anywhere ... Justin was eventually arrested on suspicion of violating the protective order prohibiting substance use.

As for why Lyssa called the cops in the first place ... we're told she was informed about Justin through a third party and felt compelled to report it. That said, there have also been rumors Dog is actually dating Justin's mom, Moon, who's a family friend. Dog has denied such claims, saying they're just friends, but we're hearing his kids aren't convinced.

Of course, Dog's wife, Beth, died from cancer last year ... so him moving on so quickly might not sit so well for some.