An NU bearing is used as a "free end" bearing where there is no axial load. An NJ bearing can take a limited amount of axial load (thrust). Choose the type that satisfies the axial load or radial load only. Yes the NJ can be used. If the motor is driving a belt system, depending on the alignment of the belts, an axial load could be imposed away from the motor or towards the motor. The NJ bearing would be the one to use, but it would have to be set so the axial force is toward the thrust portion of the bearing.