Agree with Greg, if you want to give it a shot, configure a repository on ISE and map it to server of your choice.
then go operations>reports>reports>Endpoints and Users>Radius Authentication>logged at (select last 30 days), it will give you a warning (The report may take a long time to run. Would you like to run it in the background instead?) click Yes and point it to your repository on ISE.
-hope this helps-