Thanks for posting to our Testing Tools forum.
While I cannot comment on Selenium's support for our RadControls, I can share that Telerik has an automated testing record / playback tool called Test Studio. Test Studio includes native support for Telerik's RadControls for ASP.net AJAX, Silverlight and WPF. In addition to the auto-detection of our controls, we also offer extended verifications to easily verify usually complex scenarios.
We have a 30 day trial of Test Studio you can download here. You can also download the free Testing Framework - both are great alternatives to Selenium and provide great support for Telerik's controls.
the Telerik team
for a live 'What's New in Test Studio R1 2011 SP2' event on Tuesday, July 19 at 2pm EST!
Have you looked at the new Online User Guide
for Telerik Test Studio?