I have for years played with Hyper-V (and other Virtualization technologies) in large and small environments along with Clusters SCVMM and other stuff, more and less complex environments and have come to this simple conclusion when it comes to attaching drives as physical devises, it may work but I would not recommend it.
The whole point of virtualization is that you should be able to move a VM from one host to another without doing anything to the VM. If you create a VM and attach specific physical things (like drives) from one specific host and that host fails you are toast. So no matter what virtualization technology you do use make sure that you don't do what you are trying to do.
I like you are running OMV on Hyper-V and this is how I run mine.
One VM and three disks (normal vhdxfiles of various sizes all dynamically expanding), OMV just for the OS 10GB, Docker 50GB, Media 1TB.
Make sure you set your network adapter to a static MAC address, when moving a VM without that settings things can get messed up.
When OMV is installed install "the drivers" for Hyper-V: apt install hyperv-daemons
Thats about all.
Now for redundancy... IF you want your OMV to be placed on redundant drives you have a couple of options.
On your host you can make the drives redundant and then place the vhdx files on those drives.
If you create vhdx files on separate physical drives on the host you can have OMV use all those files and use those for some form of duplication/raid.
If you have more than one host you can use Hyper-V replication between the hosts.
I opted for none of those solutions.
For simplicity I don't have anything like that, I just export my OMV one a week to a different drive so that if anything failes I have a full copy of the whole VM on my Hyper-V host. If my house burns down I have a copy of that drive at a friends house, just a simple FTP site I access using VPN.
So in my case if my hardware failes, all I have to get is another hardware with enough space to run my VM and I'm good to go. That is far simpler than anything I have ever tried before.