We have successfully be running the ctp with windows server 8 beta since the ctp was released. So when WS2012RC came along we took a couple of machines and brought it up. We can "live nothing" migrate machines from WS8Beta machines to WS2012RC and back. But cannot create new vms in VMM 2012 CTP running in a WS2012RC VM hosted on a host running WS2012RC.
Thank you,
Jeff Landry