Here are the recruiting regulations for 3 of the 5 branches, to show you that you are incorrect in your first statement.
Army: The Army's Recruiting Regulation, 601-210, paragraph 4-8b: states that* any "applicant who, as a condition for any civil conviction or adverse disposition or any other reason through a civil or criminal court, is ordered or subjected to a sentence that implies or imposes enlistment into the Armed Forces of the United States is not eligible for enlistment."Air Force: The Air Force Recruiting Regulation, AETCI 36-2002, table 1-1, lines 7 and 8, makes an applicant ineligible for enlistment if they are "released from restraint, or civil suit, or charges on the condition of entering military service, if the restraint, civil suit, or criminal charges would be reinstated if the applicant does not enter military service."Marines: The Marine Corps Recruiting Regulation, MCO P1100.72B, Chapter 3, Section 2, Part H, Paragraph 12 states: "Applicants may not enlist as an alternative to criminal prosecution, indictmenyt, incarceration, parole, probation, or another punitive sentence. They are ineligible for enlistment until the original assigned sentence would have been completed."
Secondly the supreme court has ruled several times that juvy records must be revealed for military applicants. While felony conviction can be waived, participating in a forcable rape is not one of those for most branches.