To answer your question, technically the answer is no- closing with the SumTotal exit button is not essential to the course reporting.  Once the course window is closed, it appears that a “terminate” command is sent to SumTotal regardless of how the course was exited.  The completion status is triggered at the course-level: marked as “incomplete” upon launch and, with Presenter courses, the “completed” status is triggered when the slides hit percentage is achieved, which in turn triggers the SumTotal completion pop-up window.  It may be the case that Presenter not only marks completion at this point but also terminates the connection with SumTotal (meaning if a student back-tracked through the course and took a quiz again, that the second attempt’s score wouldn’t register in SumTotal).  Regardless, this shouldn’t impact the closing of the window via the red “X” or any other way.