I was just helping a client with almost the same issue (8-bit RGB TIFF, saves as rectified black TIFF) and found the same fix, but I was setting 255 as the nodata value. You actually can still use this file, but you have to set RGB stretch to not-None in ArcMap and this doesn't help you at all outside ArcMap.
I didn't get any joy out of changing the environment settings, mostly because I believe they only apply to geoprocessing tools.
My Google-Fu failed. Does anyone know of a way to set the default nodata value in the Georeferencing - Rectify - Save As dialog so that you don't have to reset it for every single rectification?