When you create a CSR, there is no "IP Address" involved. The CA doesn't need, nor care, about an IP address. The "common name" is of utomost importance.
When you generate your CSR, the "common name" will be the "name" that needs to resolve (via DNS) to the virtual IP of your WLC.
For instance, you request a common name of "wifiguest.mycompanyname.com"
Your Virtual Address "may" be configured like so (as an example)...
When a client gets "redirected" to wifiguest.mycompanyname.com, your cert with the matching Common Name, will now be applicable to this URL.