Looking at the ProFTPd: ShowSymlinks and the ProFTPd configuration files ('/etc/proftpd.conf', the files in '/etc/proftpd.d/' and the '/etc/xinetd.d/ftp_psa'), symlinks should be visible.
This might be a case of partial FTP client incompatibility.
To instruct ProFTPd to use a different symlink syntax (which is apparently preferred by FileZilla and perhaps other FTP clients), add the following to a new ProFTPd configuration file (e.g. '/etc/proftpd.d/symlink-compat.conf'):