Same problem here. I know how to create certificates, and I'm able to upload certificates through either the web UI or the CLI. I can get my certificate set as the "Current Server Certificate". But this certificate isn't the one used for the web management portal.
The self-signed certificate that is used (with CN = instant.arubanetworks.com) is not even listed in the "show cert all" command, which leads me to believe that no amount of tinkering with the cert commands will get this to work.
Is this a shortcoming (and security vulnerability) in the Aruba Instant OS?