I don't have an answer to your question, but why not virtualize OMV ? (at least the OS portion of OMV?)
I have a 4 node proxmox cluster which has both local storage (spinning drives and SSD) and central storage via two FreeNas machines which provide VM storage over ISCSI multipath + CIFS for backups & ISO storage.
I have three instances of OMV running within the proxmox cluster. All virtual and using different combinations of storage.
instance 1) All local to proxmox node 2 with the main OS virtual and two spinning disks passed through directly to the VM
instance 2) All local to proxmox node 4 with all disk virtual (I actually have the docker plugin running on this one just for testing)
instance 3) All disks including the OS connected via ISCSI - this one setup using HA and moves from node to node
My Proxmox hosts: Dell R710, 2x R620, 1x old custom built LGA1366 system. In each machine I have a hardware raid card running with 1gb cache presnted to proxmox as one single disk. Spinning disks setup as raid 10 and SSD setup as raid 5. About 100gb or ram in each system. All have dual 10Gb SFP+ Nics; Standard EXt4 format with LVM thin for local vm storage; ISCSI multipath for central storage ... setup as either LVM on proxmox or entire lun passed directly to VM
I guess what I am getting at is that the performance from OMV in any one of the scenarios is pretty good.
Definitely hits full gigabit speed ...... not full 10gb, but that is a different story ...hahaha
Depending on the OMV instance, I have different plugins running and they all work fairly well. Before I switched my central storage to FreeNAS, I used to have two OMV systems running. Now that they are virtualized, I can't tell that much of a difference in performance...... just in available storage space