I haven't seen it mentioned, and using the marines may be a stretch. Regardless I noticed that they have another piece of shoulder armor that, to my knowledge, we don't have. Not to mention that they seem to have whatever equipment pieces combined in whatever fashion, much like the spartans at the end of the game.
I'm basically wondering if players and npcs share this customizable aspect. If so it could probably be assumed that whatever you see you can get. Though I'm pissing in the wind here, so yeah.
This also reminds me of chess. When you play the character with said armor well they are either elites or nonexistent. I'm basically wondering if that is caused by it actually needing unlocked and there's like a conflict or something.
Again though, pissing in the wind, and enjoying it.