Thanks EdT. It took a little while, but eventually I looked at creating a new WinPE disk, but based on the Windows 8.1 (32 bit) environment (I believe this is PE 5.1), and it worked flawlessly (well, the clone operation works, but as the initial build runs the console in WinPE and as I'm cloning a Windows 2012r2 machine, I don't have the console application added to the actual OS as GSS no longer seems to work for this OS, so the Ghost Console looks to reboot the machine and detect the new OS, which of course fails).
In relation to the original question relating the the VMXNET 3 NIC, you still need to add this to the PE image, however, a VM with E1000e NICs had no problem in discovering and installing the correct drivers.
I think that the underlying issue with the original PE image with GSS was not that the VM used the E1000e NIC, but rather there where two of the same NIC installed on the machine. I have booted a VM from the original PE image with a single E1000e NIC and seen no issues.
For reference I have attached a small set of batch scripts that might act as a starting point to build a WinPE 5.1 image. You still need Windows ADK with Deployment and PE environment installed from Microsoft, but the script should then make a NEW image, once you have copied you GSS file to the sub folder. This is far from perfect as I would like to modify the script to detect an image that has already been extracted and modified that you simply want to add files to, and question user as to what kind of image they want to create (such as a console, or direct Ghost Cast server session), but its a start. I will also post this to the thread you points me toward. Its also taken from a 64 bit based machine so paths names (the the 'Program Files (x86)' folder) might be different if you run it on 32 bit machine.