Definitely not in the prototype/demo. I don't think they even implemented proper character model for the player until few months back in the upcoming Steam version. I haven't seen any screenshots showcasing 3rd person mode so it's not in at least not yet but it at least should be possible to add it now.
Bump - does anyone know if this will be possible to do in the Steam version? I primarily play survival games like Ark and such in 3rd person so I can zoom out and look around my character with a larger field of view. Will this be possible in the Steam version of Raft?