I assume you want to do floating tapping? as rigid tapping requires an encoder on the spindle and a controller to gear the Z axis to it.
You cannot plug a motor the way you would do it with contactors, the VFD must have control at all time.
Depending on the HP and the size of inertia of the spindle, you may find you need brake resistors to dissipate the reverse energy of rapid decel.
Output of a VFD is not 'pure' sine wave as it is composed of a PWM signal.
Also you did not mention if the machine is manual or under CNC control?