I Have a Question

I would feel that it means the same for anyone who has been hiding what they feel inside. When you come out of the closet you are opening the door to let anyone else know what you feel inside.

You could apply it to any secret, really

You get to define your closet. But I would suggest if you say you are coming out it would be wise to explain what it means to you.

I'm a closet army

I think it applies generally to making a previously secret activity public but I think usually applies to publically acknowledging being LGBT. I’m not sure actually which usage came first.

You could use it for any secret....I’m in the closet to most people about being bisexual and about being a nudist.