Custom Configuration Services for custom imaging does not configure any systems, its what the customer would ship to Dell for deployment.  If MBR format is still required in your environment, then yes two images would be required.  The caveat with building MBR formatting is that there is a limitation on hardware, for ex: Follow on from Sky Lake, the Kaby Lake processor chip set only supports Win_10 UEFI.  If not environment limited, going forward with all UEFI would be the way to go. 
I'm trying to build a Gold Image to submit to Dell Factory manufacturing for my employer (University of Rochester). I've been able to capture a number of .wim files which always test well in the Hyper-V environment using Gen1 VMs (MBR). However on the Venue Pro 11 (meant to test for UEFI hardware restore), the .wim is applied and on reboot the boot files cannot be found and it just hangs. If I force ImageAssist to bring up the CMD window I can manually run a BCDboot command to copy UEFI boot files to the drive, reboot and it goes straight through to the first time login screen. I need some guidance/consulting on how best to capture from a VM that will allow me to then apply the .wim to ANY format of Dell hardware (MBR/BIOS vs. GPT/UEFI). It's not clear to me if I need to capture 2 different .wim files (one from Hyper-V gen1, then one from Hyper-V gen2) and supply those to Dell? I was hoping we could get one .wim file to work with the Dell Restore Tool on UEFI or MBR fomat computers. I'm curious to know what's the best path. Thanks.
ImageAssist .wim file restored to Venue Pro 7140 UEFI won't boot