I've been using Xcp-NG and Xen for awhile now and unfortunately i have had to change everything from Xen to Esxi because this feature is not there. hypervisor.cpuid.v0=false is the only line I have to enter for it to hide the GPU's in all our servers.

It's a shame as i understand it isn't a priority but this has been asked for many years from the google searches i have done. When this feature is available I will come back to Xen unfortunately until then I have to use Esxi