I managed to get Hiren BootCD 1.0.2 working on UEFI (Only tested in Hyper-V 2019 Gen. 2) by using the following config:
set tftp-path tftp://${fog-ip}
set http-path http://${fog-ip}/images/tools/hbcd102
kernel ${tftp-path}/win/wimboot gui
imgfetch --name bootmgr.exe ${http-path}/bootmgr.exe bootmgr.exe
imgfetch --name bootx64.efi ${http-path}/efi/boot/bootx64.efi bootx64.efi
imgfetch --name BCD ${http-path}/boot/bcd BCD
imgfetch --name boot.sdi ${http-path}/boot/boot.sdi boot.sdi
imgfetch --name boot.wim ${http-path}/sources/boot.wim boot.wim
boot || goto MENU
The key was to add:
imgfetch --name bootx64.efi ${http-path}/efi/boot/bootx64.efi bootx64.efi