My son is a cadet officer in Civil Air Patrol and has been very active. Is it a good idea for him to wear his dress uniform to the nomination interviews, or would it be best to wear a standard suit and tie?
Suit and tie. Wearing a CAP or JROTC uniform might come off as pretentious. Generally you will be interviewing with a board of former or current officers.
I would give a different answer if your DS was active duty enlisted. In that case I think a dress uniform would be appropriate as the board will know from his application that he was already serving.