Don't want to start a fight, but I don't think that's legal...! Unless I misunderstand, anything killed in gun season must wear a gun tag regardless of what it's killed with. I'd be a bit nervous if I was him.
You can use an archery tag during rifle season as long as the game is harvested with archery equipment. I believe you can even have more than one method of taking game in the field as long as you have the appropriate tags to do so.