You can add your own style templates and use them in TinyMCE the same as in FCKeditor. What you can't do is add toolbar items for things like font size colors etc whereas in FCKeditor you could override this by the custom config file and add those items to the toolbar. For a CMS its a bad idea though because you will then have your users creating hard coded styles in your content that are not subject to skinning. To have a skinnable site where the style changes complately by changing the skin you must use only css and no hard coded styles. The hard coded styles that your users enter into the system will still be there and may look awful a year from now when you design a new skin and those hard coded styles don't match the skin.
Style templates allow you to define css classes that your users can apply from the style dropdown in the editor. Then if you later make a new skin you can change the style rules accordingly in the new skin for the same css classes.
The CKeditor looks like it has a config file but not the same as FCKeditor, not much in there and no clue how to configure it because there is no documentation about it. As soon as I learn how I will be removing the unwanted toolbar items from that editor as well. For now I consider it an experimental editor.