Currently we have native support for the standard Silverlight controls that come with Silverlight 3. We also have native support for our RadControls for Silverlight. We plan on adding native support for the controls included in the Silverlight Toolkit add-on in a future release. This should not prevent you from testing the controls using the tool in its present form however. We'll see the various base components that are used to makeup the more complex Toolkit controls. You should be able to perform your testing against these base components/controls.
the Telerik team
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items