I don't think vibration would have much, if any, effect on effeciency of a motor. It is more a symptom of some other problem. Some examples are eccentricity, imbalance, misalignment, rotor bars, bearings, looseness, etc. These problems will have an effect on motor life and possibly performance.
Suggestion: There are various motor vibrations. Some of them are motor inherent and cannot be removed. They are caused by the manufacturing tolerances. Therefore, the efficiency on the nameplate is aligned with these motor vibrations. Obviously, if the motor vibrations deteriorate the motor operation and motor load operation, the motor efficiency decreases and motor-load set efficiency also decreases. This is because of mechanical dynamics absorbing more watt energy than it was at the new motor operation. Also, friction, e.g. bearing, will somewhat increase (including the bearing wear-out). Some large motor-load sets have vibration sensors that stop the motor if the vibrations exceed a setpoint.
