Though Bing Imagery is not officially supported in ArcFM for Silverlight 2.2.1, there were some changes in our 2.2.1 client code to allow our Map Inset tools, client-side Print Templates, and Row Details viewer to work with it (though it may require the WGS84 workaround).
Bing Imagery can be added to the Silverlight page via page.config:
<Layer MapServiceName="Bing" LayerStyle="Aerial" ServerType="Production"
Visible="True" Type="BingTileLayer" />
Note that as of the 2.2.1 ArcFM for Silverlight SDK release, Bing Maps are undocumented, not thoroughly tested, and that the Configuration Tool has not been updated to support them.