"Sounds plausible, but then Moodle database doesn't allow for being an Offline Activity (unless I missed a setting)." When setting up the assignment, all you have to do to make it "offline" is to remove all the checkmarks for Submission types. Moodle will then automatically treat the assignment as offline.
"Also, an Activity/Advanced grading/rubric solution will probably not allow for exporting to a CSV file." Granted, no built-in export to CSV, but since the rubric data is there and available in your Moodle database, install the Ad-hoc database queries plugin, create a query that digs out the info for you. The nice thing about this method is it can be setup to run on a defined schedule and export a csv report or email it to a defined email address.