If the engines are still turning (windmilling) they will still provide some hydraulic pressure. But the system may not be at the pressure and flow it would be with the engines running. So the flight controls would not react the same which could make the aircraft harder to control. It really depends on the airplane. Older Boeings had "manual reversion" on some of the flight controls. It was a cable from the yoke to the flight control surface. The 744 doesn't have manual reversion but each of the 4 hydraulic systems has a backup pump to pressurize the system if the engine driven pump is inop. But on some 744s some of the backup pumps are driven by engine bleed air so if the engines fail there would be no hydraulic pressure in that system. You would lose the outer ailerons and elevators but the inner ones would still be powered so the airplane would respond slower to flight control input.