If the organization already has an SSL certificate for their domains, would they need to purchase additional certificate from Adobe (with the help of DigiCert) to get CNAME setup?
The CNAME setup has nothing to do with your website's SSL certificate.
The SSL certificate enables your website to be served to your users' web browsers via a secure HTTPS connection.
The CNAME setup is to allow Adobe's tracking servers (2o7.net) to be recognised as subdomains of your own website.
So yes, you still need to go ahead with the CNAME setup.
Yes, have already raised it with the Client care and awaiting for their response. Meanwhile thought to check here in the Analytics community.
Thank you for your inputs.