You are entirely correct that Cpanel's FTP and Centova Cast's FTP are in conflict for port 21
In order for cc-ftp to work alongside a second FTP server, it would have to be set to listen on an alternate port (we usually recommend port 2121 as alternate).
Using a unix based text editor such as vi or nano, open the cc-ftp configuration file:"/usr/local/centovacast/etc/cc-ftpd.conf", and locate the following line:
FTP_PORT=21
Change it for:
FTP_PORT=2121
Finally, if you are using a firewall make sure to add your new cc-ftp port to the exception list, and start cc-ftp by using the command: /etc/init.d/centovacast start-ftp