The reason D.J. does not get any punishment is because of the following:
1. Jesse should never have left the tape with his jingle unattended in his room. He should have stashed it into his closet and/or submitted it to the advertisers immediately after finishing it.
2. D.J. did not expect the tape would have anything recorded on it.
3. Nobody even told D.J. that Jesse and Joey made a jingle in the first place.