The DSO is only available on the operational honours lists as it is a gallantry award relating to leadership in a specific operation (and is available to all ranks, in theory anyway)
As an aside does anyone have any info on what is the most junior rank in any service to have received a DSO in the modern era, which I define as post -1993 when the criteria were redefined? I once mounted a DSO group to a pilot officer who had pulled his wounded navigator from their sinking Beaufighter and had swum several miles to shore with him in tow. With the criteria now being 'highly successful command and leadership during active operations' I cant see anybody below field rank (or equivalent) getting this award now, let alone anyone from the non-commissioned ranks. As you say "in theory anyway"