A court martial is regulated by the UCMJ (Uniform Code of Military Justice). Nowhere does it say that admissions or confessions must be given under oath to be admissible. Such a requirement would eliminate 99% of all admissions.
In the response that "jagusafr" just sent to me regarding my original question to him (post #26) there appears to be at least one exception to what you're saying.Given that he's a lawyer,a former military lawyer at that,I'm inclined to accept the accuracy of his statement.I don't understand the logic behind the concept he was describing but then there's very,*very* many things about the law that I don't understand so I'll just add that to the list.