I am beginning to be persuaded you are right. However, I have seen some posts about putting vmware either on the SD card or internal usb stick that made me think the SD card could be addressable. If Dell has this limited to Dell flash cards instead of a regular SD card that might explain some of what I am seeing.
You can get an Internal Dual SD Module (IDSDM) addon for those machines - they are different to the iDrac based vFlash card. And yes, you can boot a hypervisor from the internal SD card.
Also, apparently, neither the vFlash slot nor the IDSDM are hot- pluggable.
P.