Can your employer find out anything about your military record with or without a signed waiver from you?

In my 8 years experience in Human Resources, specifically in the field of Recruiting/Staffing, I can testify to the fact that employers can only verify military service through a DD214. Of course through credit verification and address verification we can easily determine if falsification has been deliberatly given. But overall, the DD214 is the main source of verification.

There's one other way

Courts-martial convictions appear on your criminal record, and some employers run criminal records checks.