I tried the Cross-Platform version on my iMac running 10.8.2 Mountain Lion (ML) and encountered a “Bluetooth error” message upon startup (e.g., Bluetooth failed to initialize. There is probably a problem with your local bluetooth stack or API).
I did find a company (Primate Labs - http://www.primatelabs.com/wiinote/) that produces a software that connects with wiimotes using Bluetooth. They were successful in coding their software to work with Mountain Lion releasing their latest version (0.4.0) in August. Perhaps there may be a coder/programmer out there who could take a peek at the Wiinote software’s script (e.g., how does it work within ML and connect via bluetooth and the wiimote device?) – and port the same code over to the wiimote whiteboard application.