Two years later and I just ran into this on a Dell Latitude 5330 with a Dell USB-C to Ethernet adapter.

Here’s my summary,

Using the latest bzimage, FOG was able to use the registered the passthrough MAC that is baked into the BIOS.

Image capture and deploy went fine, but everything FOG related in Windows reported that the client wasn’t registered. Because I didn’t check for a driver for the USB-C to Ethernet adapter, windows used the generic Microsoft driver for the adapter and FOG (and all of windows) sees the USB-C to Ethernet adapter’s MAC address.

As soon as I installed an up to date Realtek driver, Windows started using the BIOS passthrough MAC and everything works as normal.