With that setup it'd be a shame to not run OMV virtualized in something like proxmox. As other posters say, it's pretty overkill just for OMV. I ran OMV bare metal for years but took the plunge into virtualizing it 2 weeks ago and the results are impressive. Passed through a PCIe HBA card to the OMV VM and I even have HDD spindown and SMART data natively in OMV.
Even if you have no intention to run any other virtual machines on Proxmox, the ability to make snapshots and full backups of a OMV VM is great IMHO. Being able to run other virtual machines concurrently is actually quite useful and opens up doors for learning new things.
The major con of proxmox was the learning curve - It was something new for me and it took 5 days to get it working as I like. The gigabit network performance is excellent with the paravirtualised networking - within margin of error compared to bare metal. It's also fun to passthrough a GPU to a Windows VM and game on the same machine that is concurrently running your NAS.
If you go down this route, maybe Google your intended MB to see if anyone had issues with IOMMU (Needed for PCIe passthrough).