Anyone at Gitmo is "taking no active part in the hostilities", and hence is a person who "shall in all circumstances be treated humanely".
Article 3 doesn't restrict itself to only uniformed people, or only conventional soldiers, or any other similar group. Anyone who isn't fighting is covered, lawful combatant or otherwise.
Whether you think this is a good idea or even whether this will represent a significant change is another matter, but I'm pretty sure that's why this applies to all prisoners held by the US.
Once again, they were not uniformed and they are not part of a signatory nation. So they are NOT covered. This is a penumbra by SCOTUS that is unsupported by precedent either here or elsewhere in the world that I can tell.
Ummm. No, that's a word game. If they were taking no active part when they were captured (i.e., are noncombatants), then it would apply. If they were part of a formal military (as defined elsewhere) and had laid down arms or were hospitalized, when they surrendured, it also would then apply. Any other reading makes the statements meaningless.
The only reason the Gitmo detainees are not "taking part in the hostilities" is because they are confined.
As soon as they are released, they will resume their hostilities. This has already happened with released prisoners.