When using any version of Mac OS X Server to serve sites with Web Services, you can enable SSL on multiple sites that resolve to a single IP address, but only the certificate of the first listed site will be used. This is due to a fundamental limitation of how SSL works.
When users connect to the other sites at the same IP address, they'll receive an error message like this:
Could not verify the identity of the site www.example.com.
To resolve the issue, use a unique IP address for each SSL-enabled site.
Background: When an HTTPS connection is initiated, the two hosts first set up an encrypted transport and then send the request to the server for the website. The web server won't know what hostname is about to be requested until after the encrypted transport is established. Because there is no way to change the encryption mid-connection, there is no way to change the keys used.