Unfortunately, it is not possible to use the built-in RadEditor submit and cancel buttons in MOSS. However, I think that your request will be covered by a feature we plan to include in the next editor web part. The feature will alert the user when they try to navigate away from the page without saving the editor content. This way it will be easier to remember to click the "OK" or "Apply" buttons in the web part menu on the right side of the page.
All the best,
the Telerik team