No, Sketch is the only move that will allow you to learn an opponents move, so Protect will not teach Smeargle Roar of Time. Also, Sketch will not permanently teach a move when in a WiFi battle - only during the battle. Any moves Sketched during a WiFi battle will revert back to Sketch. For legendaries, yes, you may sketch any move the Legendary used, no matter how crazy the idea of Smeargle with Roar of Time is.
Sketch can do any move other than Selfdesruct, Explosion, Chatter, Struggle and Metronome. (as of Gen V). Anything other than those few can be learned, no matter the circumstances.