I don't think it counts as a hypervisor because it's basically running multiple user land environments on the same kernel. But yes, the video output is already used by android so if you need graphics it goes through vnc. Maybe that's possible to bypass on a routed device.
I don't know about all solutions but Linux Deploy for example creates a chroot environment and runs the Linux distribution from there. That means that the distribution's process are running alongside android's process on the same kernel. No translation, no abstraction, directly on the kernel that runs android. As far as the kernel is concerned, the android launcher and the Gnome environment are equal resident.
Yes, it works very well because it is not a VM, android is already running on the Linux kernel.
Contrairement à r/France, ici je lis tout les commentaires des megathreads