They have the same vibes. Both got dark sunglasses and are shown separate from the rest of the crew.
Im not sure if Kyo really was a marine like people theorize. It’s possible he could have just been a bounty hunter or some strong fellow. But I do think he has a strong code of Justice, generally dislikes pirates, and only joined Rocks due to a much greater dislike of the WG.
I think he definitely betrayed Xebec in the end.
