The overview map works whatever the layer provided that the spatial reference be the same than the main map.
Re: the sample at http://help.arcgis.com/en/webapi/sil...tm#OverviewMap
Switch to the XAML page then the Live Sample page, and note that the overview map initially does not draw. You need to pan/zoom the map before the overview map initialises.
This also happens when I compile and run this code locally. Any ideas why the overview map doesn't show immediately?