Customer might be using hostname SSL certificate, instead of IP SSL certificate which is fine. Both, IP address and host name are valid Common Name in the SSL certificate. In both the cases, the SSL certificate is for the internal networks or intranets.
In the Vantage Installation Report, IP address reference is present because that is the only thing Vantage Installation is able to figure out on that level. This hostname/IP SSL certificate is resolved one level up so the customers need to figure out by themselves. Also on OMVS the following command gives the DNS hostname and corresponding IP address.
Usually the organization uses one type of certificates - either IP or hostname - not both of them together so in this instance customer need to use the DNS address https://xyz.server.net:nnnn/VantageGMI/ instead of https://xx.yyy.zz.mm:nnnn/VantageGMI/ and it is fine - all is correctly set up.
IP SSL certificates are even less commonly used than hostname SSL certificates, because they are less flexible. If the customer have an IP SSL certificate and want to move customer's website to a different server with a different IP address, then customer would need to obtain a new certificate. However, if the customer have a hostname SSL certificate, then customer can simply update their DNS records to point to the new IP address, and their certificate will still be valid.
In general, it is recommended to use the hostname SSL certificates over the IP SSL certificates whenever possible, as they provide more flexibility and are easier to manage.