It would show as many GPU as phisical procesors available.
Also what performance could I expect from one VM with a passed through GPU?
Regarding the use of GPU full , other performace depends of other resurces alocated for the VM. (disk, memory,...)
With passthrough does NVENC work in the VM?
With the use of docker you can do as 20 nvenc per GPU... with K1,, we do 14 max with K2200 (1 GPU visible and passed thru to one machine)