Hi Rick,
We're aware of the issue. Map control gets it's spatial reference from the first layer added to the control which is usually the underlying basemap. It's something we're looking to fix in the new Runtime SDK for .NET
For now I would suggest to load a dummy layer with the spatialreference you need and unload the layer once the map is initialized.
After that you should be able to use graphicslayers with out a problem.
Regards,
David