But they would be required for him to connect with DFUse to rue-load a firmware to be able to talk through Granity since the SimuCUBE firmware locks out the Granity access.
No, since the Dfusedemo software is connecting to the X3 port, which can be made visible as STM32 bootloader. It seems this port has some hardware related fault.
FTDI drivers are only needed in some rare cases when user wants to access IONI servo drive via the X4 port, which actually has a FTDI serial to USB chip on the Simucube.