In what way do you want them to be able to edit the menu bar? By adding pages to it? How would the pages be created? I'd like to understand your question better before giving the wrong advice.
I think you can probably do what you want by using the "create page as template" functionality in powerCMS and then using a recordset to get the template pages and add them to a menu... if that describes what you want.
It sounds like there could be a bug in the 'create site sculptor page type' functionality. I'll report it to have QA look into for logging a bug.