Hey Stephen. Thanks for the note; it may be possible, but it’d definitely require some hackery. The Gravity Forms solution is more a third-party hack than an officially supported method of soliciting frontend submissions. But when our Community Events add-on is released (sometime between now and the end of March), it will allow for frontend users to submit recurring events (if the site is running PRO) right out of the box.
Sorry I couldn’t offer up more here. Let me know if you’ve got other questions along these lines.