The impulse response of REW is not created with the mic calibration file included. The cal file is added when the response graph is created. This allows the user to remove or add the cal file later using the IR Windows Apply button.
All that said, I then highly doubt that the cal file is added to the impulse response on Export. It would be the raw impulse file without cal file added.
John can certainly correct me on that if I'm incorrect.
brucek