The EditorWidget sets its own datacontext with an internal editor based on the properties you provide like Map, GeometryServiceUrl, Continuous, Layers, etc.. some of which are properties of the Editor as well.
If you set just the EditorWidget's datacontext to the editor, all of their common properties will get their default value. The widget does not check if its datacontext has been set to an editor and populate its properties based on this.
So if you would like an Editor defined as StaticResource, instead of setting EditorWidget's datacontext.. you can do GeometryServiceUrl={Binding Source={StaticResource MyEditor}, Path=GeometryServiceUrl}. In this case, you still need to grab the internal editor the EditorWidget created for itself to subscribe to its events.
Jennifer