I was using Services to call ArcObjects such as Server connection and CreateFeatureWoekspace. You have two options to get ArcGIS server connection, by using ESRI.ArcGIS.ADF.Connection.AGS.AGSServerConnection or ESRI.ArcGIS.Server.GISServerConnection. When connection established, you can create server context by using ServerObjectManager. After server context is ready, you can enjoy ArcObjects..... Once should know is to save the context to session variable so you do not have to recreate in next service if session still alive. You need to following property for your services
[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Required)]
Once your own ArcGIS services are ready, you are ready request from silverlight.
Good luck!