Is there anyway to round trip files from FCP to Motion without export or use original files

There is no round tripping in the traditional sense but the present system is vastly superior. Create whatever effect you want in Motion and it will be available to use in FCP X to use in as many clips you want. Publish effect parameters in Motion and adjust them at will, including using keyframes, directly in FCP X.

If the media is outside the library, stored externally, you can use in it the Motion, either creating an effect template or by exporting from Motion.

No, that feature is not present. As I said, there is a different workflow.