I wrote up a web config script to supplement the one that comes with proftpd, that has user view, add and delete.
I created it to help myself easily admin from GUI. Use at own risk.
Download from: http://pastebin.com/e7QKbUvE
Place file: /mnt/DroboFS/Shares/DroboApps/proftpd/www/index.php
Backup your passwd file first from within proftpd.
For ProFTPd listed here: http://www.droboports.com/app-repository/proftpd-1-3-4b