That's BS. They are asking if Barack Obama is constitutionally qualified to be the CinC of the US Military. Lakin is seeking to whether the US Constitution is being upheld, which is the converse of NOT trying to overrule it. And the US Army would not be the "final arbitrator" that would be the people of the United States to whether Obama is a lawful or an unlawful president.
Entirely correct. (One seldom gets gets to use that phrase when addressing a Birther.) And just how do the "people of the United States" express their opinion? Through the actions of the Congress of the United States -- not through the United States Army. Birthers can chase their tail around that fact until they drop, but they are never going to catch it.
Oh, and if the orders deploying LTC Lakin are void, 'cause BO is President, then the orders convening the General Court Martial of LTC Lakin are void, 'cause BO is President. And what jurisdiction does a "court martial" not convened by a lawful order of a competent authority have? None.
For Birthers, the half full part of that glass is that LTC will have a (specious) ground to file a writ of habeas corpus challenging his confinement. The half empty part is that a void court martial doesn't have any jurisdiction at all, much less the jurisdiction to remove the President of the United States from office.