It depends on how you have it coded, there is a config mode that will automatically add <head> and <body> tags so you could take that and either use php/asp/whatever to write it out to an html file as a way to save it, but it depends greatly on the design of the cms, some content mangagement systems use database driven pages entirely, others use combinations of both mixxing systems like smarty or other templating setups. I don't see any reason it couldn't be used as long as the cms is in a language supported by ckeditor.
Re: Using CMS to add a new page to an existing web site