The RadRotator custom buttons, once attached to the control, will stop doing postbacks. This is an expected behavior as rotator buttons are required to only change the currently displayed item.
Still you can attach to the OnClientClick event of the image buttons and within the handler initialize an Ajax request using RadAjaxManager. You can review the help articles on using this control and particularly the one with initializing custom Ajax requests - http://www.telerik.com/help/aspnet-ajax/ajax-add-ajaxrequest-to-client-event.html
Hope this helps.
the Telerik team