Unfortunately, the current version of the tabbed viewer does not have the ability to read the scalebar settings saved in your organization account. In order to change this, you will need to download the code and, modify the scalebar units in the Map.js file, then host the code on your organization's server.
In an upcoming release of ArcGIS Online, we will be replacing the tabbed template with a new version that provides many more options and should handle settings stored at the organization level.
