Hello Fraeco,
You can verify that the DigiCert certificate is in the root certificate store by looking in the MEBx on one of the machines.
You will find a Option to list the certificate store there.
Are you trying to Provision the Clients via SCCM 2012 R2?
If that is the case and the AMT Version of your Clients is greater Version 8 SCCM can't provision them.
You Need to get the Intel SCS Tool (Version 9 or greater, download via the Intel Download Center) and the SCCM2012 Add-On(Version 2.1.5 atm, i think ).
With these in combination you can Provision the clients with Tasksequenzes. The Clients will be shown as 'Externally Provisioned' but you
can use Wake-Up and other Features afterwards.
The cause for this is, that Intel stopped using the SOAP and uses WS-Managment instead. SCCM 2012 seems to have some problems with that.
You will find a great Installation Guide in the package, that helped me a lot. A little tipp, read the Manual first before trying to install the SCS.
There are some things you have to think about, before choosing if Database-Mode or not.