The machine state would stop every time on "CustomizeOS" and eventually the deployment would time out. From the Windows machine, I looked at the guest agent log and saw that it would hang every time on Wait for completion of '10_customizeos.bat' with no other progress.
The problem was that the scripts for the guest agent (located in the c:\VRMGuestAgent\site folder) were all "blocked" and could not be executed. For example, looking at the properties of c:\VRMGuestAgent\site\CustomizeOS\10_customizeos.bat showed that ""This file came from another computer and might be blocked to help protect this computer" - with the option to "Unblock"...
I noticed that the GugentZip_x64 that I downloaded from the vCAC 6.0 appliance was also blocked - this means that the content of the zip would also be blocked when unzipped!
To fix this (or prevent it), simply unblock the zip before extracting. In my case, I took the extra precaution of removing the vCAC gugent service, deleting the entire c:\VRMGuestAgent and doing a fresh install with my "unblocked" zip.