Not NVIDIA; fly.io reimplemented the parts that CH didn't already have. I know that CH is developed on GitHub but I don't know whether the changes are public or in-house.
That said, the slowness of QEMU's startup is always exaggerated. Whatever they did with CH they could have done with QEMU.
Was that recent, with MIG support for GPGPU partitioning? Is there a public mailing list thread or patch series for that work?
Nvidia has a 90-page deployment doc on vCS ("virtual compute server") for RedHat KVM, https://images.nvidia.com/content/Solutions/data-center/depl...