Microsoft and Intel have included support for AMT firmware versions less than 3.2 with the inclusion of the WS-MAN Translator that will be released and integrated with SCCM SP1 with the release RC1. The SCCM SP1 beta today does support 3.x clients for testing validation purposes; however, there will be a hard requirement to use the WS-Translator with any client less than 3.2 once RC1 releases.
To avoid having to manually configure your internal CA root hash, you can work with your OEM to have the cert hash of your provisioning cert issuing CA pre-loaded into firmware. Other then the root cert hash of your internal CA, that should be all you need to do. Although, the default admin password will be changed as SCCM goes through the provisioning process, you can request the OEM to pre-configure the MEBx password for you. This will need to match what you configured your SCCM environment with.
Matt Royer