Check out VirtuaGL and TurboVNC. It is possible to run these two things inside a docker container, install a DE and accelerate a GUI app. I've been doing it for quite a while.
Also for all those checking the OPs original lib out. It does work and it is great and also probably the most mature option, but my understanding is that future focus for GPU inside containers is with this newer lib, also looked after by Nvidia:
https://github.com/NVIDIA/libnvidia-container
I'm fairly familiar with this stuff, though not an expert, for my startup http://realityzero.one. But, I've not been paying that much attention to this area of late, so if I've got this wrong then please feel free to correct me. Perhaps they're for different things. I know there's been some discussion from the k8n crowd about the newer lib in k8n's github issues.