You can submit your application first without the GMAT, but a sufficient GMAT result must be submitted by the application deadline, or before the programme has reached maximum capacity (whichever occurs first).
If you submit your application early (between October and December), the RSM Admissions Office can already evaluate your academic background and give you an indication regarding your eligibility, even when your GMAT scores are missing.
If your GMAT results are still missing when the deadline has passed or the programme has filled up, the application will be rejected.