Has anybody determined a solution for this?  Some individuals are getting banned correctly, but others are not (I have about 3000+ hits from one IP per day on vsftpd that cannot get banned due to the improper reverse lookup).  It seems more related to PAM after looking at the logs:

Aug 30 13:10:24 hexvader vsftpd: pam_unix(vsftpd:auth): check pass; user unknown
Aug 30 13:10:24 hexvader vsftpd: pam_unix(vsftpd:auth): authentication failure; logname= uid=0 euid=0 tty=ftp ruser=Administrator rhost=genemaxserver.com
Aug 30 13:10:24 hexvader vsftpd: pam_succeed_if(vsftpd:auth): error retrieving information about user Administrator

Thanks for any ideas,
Dan