As far as I know, it's immaterial what you decide on the Uniform Load unit in the Special Execution Parameters. Checking the box only makes it all in G's when you define Uniform Loads for the first time. Your unit selection in the Uniform Load spreadsheet would override the setting in the Special Execution Parameters. So it is expected that you'll get the same results whether or not you check the box in the Special Execution Parameters.
In older versions of Caesar, if I remember it right, you can only select the unit in Special Execution Parameters. No option for that in the Uniform Load spreadsheet. So it would have made a big difference then. Back then, for each file, you'd have to decide only one unit of the Uniform Load.