Is it illegal for a military lawyer to give legal advise to civilian clients that are not eligible?

If military lawyers are not allowed or authorized to provide legal advice to civilian clients who are not eligible to receive legal assistance then is it also unethical if the lawyer claims attorney-client privilege? A USAF colonel attorney agreed to provide legal advice to a foreign national civilian that have no association with the armed forces in which the civilian accused an active military member of alleged wrongful acts. The colonel gave the civilian legal assistance and openly claimed attorney-client privilege when asked refused to testify in trial due to unavailability and privilege. Can the colonel be brought up on charges for unethical conduct? Thank you for any response.