I have a fresh install of OMV that I am trying to get the NVIDIA Drivers working on. I encountered issues installing kernel headers so I had to downgrade to 4.19.0-0.bpo.5 from 4.19.0-0.bpo.6. Once I had that, I followed the instructions on the Debian wiki to install the drivers using apt.
After installing everything, the driver is not being used per lshw and the nvidia-smi tool. I used to have it working before but I can't remember what steps I took to get it working.