Under U.S. rules, if he was a "student pilot" it would not be legal. That much is pretty specific. If he had at least a PPL it could be legal I believe.

61.89 (b) A student pilot may not act as a required pilot flight crewmember on any aircraft for which more than one pilot is required by the type certificate of the aircraft or regulations under which the flight is conducted, except when receiving flight training from an authorized instructor on board an airship, and no person other than a required flight crewmember is carried on the aircraft.