So wait, can we still give them whatever armor we want or will this be like mass effect 2 where they only wear their own outfits and that's it?
Pretty sure you can manage their equipment with a lot more ease than in Fallout 3, so I'm fairly sure you can choose their armor. It just seems, based on some of the more recent info, that the more you advance a companions questline, the more they trust you and reveal their past.
Spoiler Since we know Arcade is former Enclave, and we've seen Enclave armor, we can assume that once he reveals he is ex enclave, he also brings the armor out of retirement. Same for Raul. We know he is a former gunslinger, and now we are seeing a "Vaquero" (cowboy) outfit.
It only makes sense that by uncovering their past, we get armors relating to that past.