I think it is fine as long as he is being treated for being good. My treat training backfired when I taught him to "trade" for when he has something he shouldn't-a coin, a plastic wrapper, etc.- so now he has learned to find anything in the house he isn't supposed to have and then flaunt it in front of us so we will treat him for a "trade". He can't even be tricked because he wont drop the offending object until he sees the treat in my hand. I have even tried to ignore the fact he has something bad to see if he loses interest, but he will toss said object in the air in front of me and grab it back up until he gets a treat, then he runs off to find something else. (Thanks Victoria Stillwell...that worked out well...
)