I finally managed to run ONTAP 9.6 sim pretty well the way someone may find inappropriate, but anyway it works, and ONTAP runs pretty smooth.
The key thing with Hyper-V is that ONTAP simulator doesn't include drivers for Hyper-V emulated network adapter, but requires e1000 as described in OVF.
What I did was:
1) On my Hyper-V host I created a Gen2 (this is fairly relevant, and Gen1 might work as well) VM running Debian 9.9.
2) On the Hyper-V host executed a powershell command
Set-VMProcessor -vmname KVM -ExposeVirtualizationExtensions $true
where KVM is the VM name as listed by `get-vm` commandlet.
This allows VMX CPU extensions to be exposed to the guest.
3) Install QEMU/KVM inside the guest
4) unzip Workstation OVA for ONTAP simulator
5) convert vmdk -> qcow via qemu-img (done on Debian Guest).
6) create VM using virt-manager. This can be also done by importing dupmed XML of an example VM.
7) allowed nested guests in KVM.
Following all these, I succeeded to run 2 instances of ONTAP sim (2 clusters with cluster interconnect). Also Windows and Debian VMs run fine on that KVM hypervisor which itself is actually a guest inside Hyper-V.
Virtualization overhead is almost not noticeable. At least as compared by Linux CLI-based 7-zip benchmark that was executed in first-level guest (VM that runs directly in Hyper-V) and nested guest (debian VM in KVM, while that KVM is a guest in Hyper-V) thanks to VMX extensions exposed all the way through.
KVM configuration and ONTAP xml of the KVM guest (domain) can be found in this thread:
Hope this helps