If someone is looking to join ROTC, should they disclose an arrest for shoplifting if they were never convicted or charged?

I will answer with two statements
1. They will run him in NCIC which has any interaction with LE entered in it, even if he was not charged, even as a witness providing a statement. Especially if fingerprinted.
2. Concealing and omitting information is worse than disclosing information with any kind of clearance

Tell your nephew to hide nothing. On regards to the fingerprint question, he needs to answer truthfully. If he answers NO and the background check comes back that he did and for why....it's gonna bite him. As for the first part, if he never was arrested not went to court, who assigned/asked him to do the counseling and community service? Either way, your nephew should hold nothing back. Omitting information, intentionally, and it being found out later will never ever turn out well for the applicant. Even if he was never arrested for the shoplifting, there should be a block for him to explain what happened.

As a minor I got in trouble. When I went to sign up I disclosed what happened. Not disclosing would have been a second mistake, and one that could have really ruined my life.