The OVA image we spawn from Generic images is designed for vmware to make booting in a Desktop environment simple, and with the sole purpose of supporting development of project GUI items like the settings add-on. Any other kind of platform or use-case is deliberately "not officially supported" to keep project maintenance simple. Over time the number of other environments it might work in has probably grown, but we do not test that image much, have no intention to start testing it much, so anything that happens to work is accidental.
In all cases LE needs to boot with a supported GPU, which is either real hardware mapped for our use, or one of the working virtual GPUs in the kernel. The Generic kernel defconfig is probably missing drivers for whatever GPU that proxmox uses; or the GPU that is there doesn't support the OpenGL video pipeline that Kodi requires.
