Since it's up to the trial judge, not the investigating officer, to evaluate affirmative defense that the orders were not lawful, it's not clear that it could be done at the Art. 32 hearing anyway.
However denying the defense any documentation relating to Obama's eligibility at the Article 32 does not bode well for their chance of getting said documentation anywhere in the future.
I've said all along. Lakin will be tried and convicted and Obama will never even enter into it.