Add will work against either an editable FeatureLayer or a GraphicsLayer. It will only be enabled if LayerIDs is only referencing one layer.

If you are editing a FeatureLayer, the CommandParameter should be the feature type to use if you have feature types, or the template name if you only have templates defined. If you have multiple templates defined for each feature type, you can use an array object[] { featureTypeId, featureTemplateName } as parameter. If no template and/or feature type is specified, the default will be used. If the FeatureLayer is read-only, Add will not be supported.

If you are editing a GraphicsLayer, the commandParameter must be a ESRI.ArcGIS.Client.Symbols.Symbol to use for drawing. The DrawMode will be deduced from the symbology type.