EDIT: Think I figured it out. Under Groups > Basic > Aruba Instant there is a Captive Portal Cert option where you can select the cert to use. Going to run that command later tonight and see if that works.
I used XCA to import my Private Key and export it as a 'PEM private (*.pem)' file. I then opened the exported Key file and pasted the text from my wilcard + intermediate .crt file and saved it, retaining the PEM format. I loaded that file into Device Setup > Certificates. Like I mentioned before, I already went to Guest Self-Registrations > NAS Vendor Settings > Ip Address and entered 'clearpass.domain.com'. I am still being redirected to the securelogin page though. Feel like there is something I am missing here.
Thanks for the help BTW, XCA was a lifesaver. Couldn't get the OpenSSL commands to work earlier.