The wheels of an aircraft DO NOT provide propulsion or forward motion to the aircraft and therefore do not 'push against' the action of the conveyor belt. Any forward motion (thrust), comes from the engines or propellers not the wheels. Forward motion/Thrust therefore is being applied to the aircraft 'body'. It has NOTHING to do with how fast or slow the wheels happen to be 'spinning/free-wheeling'.
According to Newtons Third Law of Motion, every action has an equal and opposite reaction. The thrust of the engines is acting against the 'air'. Because the wheels are free-wheeling the conveyor belt cannot exert any force on the aircraft with respect to forward motion. All that it will do is make the wheels spin faster or slower. There is no force in this scenario that is opposing the thrust vector of the aircraft. Therefore if the conveyor belt cannot exert any force on the aircraft, which it cannot because as we now know, the wheels spin/free-wheel, the aircraft will take off.
