NVIDIA GPUs still require "dummy" HDMI plugs. They won't be fully usable without something plugged in; it's not clear why.
At said $OLDJOB, we ended up soldering dummy VGA plugs that had resistors across the right pins when we wanted to experiment with building a low-power cluster of NVIDIA Ion boards and seeing how it competed with big cards. Ah, memories.
You also used to be able to edit the PCI IDs for the drivers to get the Tesla ones to attach to consumer GPUs, but that stopped working at some point.