It is not technically double jeopardy since this is an administrative proceeding and not a criminal action. However, you can use this to your advantage by arguing that the issue has already been considered by the court-martial and they decided you should not be separated. I have found this argument to be very convincing to the Board members as they feel the same way - why are they doing this to you again? I have had a number of retentions at an admin board following a court for this very reason. You and your attorney need to prepare your evidence for teh Board adn demonstrate all the reasons why you should not be separated and why hte court decided to allow you to stay in.
I hope this information helps. If you have further questions, please feel free to contact me directly at [email protected] or 757-420-9321.