I am not in the military, but I do have a security clearance. I worried that being poly may jepordize that. So I did some research. I found a document that talked about open marriages and homosexuality with regards to security clearance. The basic worry is that someone can be blackmailed. So if you are out (which is not easy in the military), you are not a blackmail risk. One senario was a gay man married so he looks straight. He is a target for blackmail. But a bisexual looking for sex with men while his wife knows is not a target for blackmail.
Sorry, but that is the only angle I can speak to since I don't know much else about the military and polyamory.