I am using v8.1 (3843236). I have setup a nested ESX 6.0.0 virtual machine on a ESX 6.0.0 host. I am running this embedded client on the host, not on the nested ESX.
The virtual machine list gives me the following warning "The configured guest OS for this virtual machine does not match the guest that is currently running. You should specify the correct guest OS to allow for guest-specific optimizations.".
However, I setup the virtual machine to use "Other" and "VMware ESXi 6.0". I did notice that even though 6.5 is not yet out, it is listed as an option.
The exact version of ESX that I am running is: VMware-VMvisor-Installer-6.0.0.update02-3620759.x86_64.iso