Using the ItemTemplate of the RadDocking control is not supported. Please, refer to our online documentation to see the full list of not supported properties - http://www.telerik.com/help/silverlight/not-supported-properties.html
Could you please give us more information what you want to achieve? I am glad to assist you further.
the Telerik team
Registration for Q1 2011 What’s New Webinar Week is now open. Mark your calendar for the week starting March 21st and book your seat
for a walk through all the exciting stuff we ship with the new release!