GoPros and other waterproof action cameras are absolutely welcome* (just make sure you have a secure strap/mount). Other waterproof cameras/phones are also welcome* as long as they have a secure strap. If your camera/phone is not waterproof, or if it does not have a secure strap, it is not recommended to bring on the raft. Whatever you bring will get wet, and you will need to be able to free your hands in order to paddle.
*Bring personal items at your own risk