Yes. Actually the ETRSi manual recommends not inserting the darkslide except when you want to remove the back since with the darkslide inserted, accidentally bumping the back unlock button may result in the back coming off; while when the darkslide is not inserted the back cannot be removed.
Since my ETRS sytem is the most complete out of my other film camera's I had wanted it to be more versatile, and this was the only thing holding me back from having be a quick shooter