Yes.  Centova Cast does not perform any licensing check on its login form or the client area, so you can set up a second domain for the reseller on your web server (configured as an "alias" or "parked" domain on the same hosting account you're using for Centova Cast) and your resellers' clients will be able to login to Centova Cast through that domain.

The "alias" or "parked" domain would need to be configured in your web hosting control panel (CPanel, Plesk, DirectAdmin, etc.).  Please consult your web hosting control panel's documentation for instructions on how to do this.  If you are not using a control panel, you can set up a domain alias by editing your Apache configuration file and adding a "ServerAlias resellerdomain.com" line in your Centova Cast virtual host.  Please ensure that your reseller configures DNS for his domain to point to your server after you set up the alias.

Note that only the reseller's clients can login at the reseller's URL; the reseller himself will need to login through your main Centova Cast URL, or he will encounter a licensing error.