Nested Hyper-V (Hyper-V running inside a Hyper-V VM) has been available for some time.
https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/user-guide/nested-virtualization
But it is one thing to have the feature for Microsoft Hyper-V and it is a different matter altogether for Microsoft to provide an API to let third parties like VMware to provide that capability.
From the link you provided, it looks like the call has to be made within the VM (it is referred to as the L1 hypervisor). I can't seem to find documentation about the Hypervisor APIs. The Hypercall is for the guest VM to call which may or may not be what VMware is using. If it is, effectively the VMware VM effectively is already a nested VM, where
the Hyper-V on host -> VMware Workstation VM monitor Hypervisor API is already a pseudo VM -> runs VMware VM.
