With Operations Manager 4.0, NetApp does supporting running it in a virtual machine in VMware ESX 3.5 and 4.0. We also support VMware HA and Vmotion. See the attached NetApp interoperability matrix showing RHEL 5 as the Guest OS. Be sure to read the alerts and notes section.
Until I hear otherwise, by certifying Operations Manager within a Guest OS in VMware it certifies any storage compatible with VMware. This obviously includes NFS datastores. The nice thing is that the guest OS running Operations Manager has no idea its storage is NAS. The disk allocated to the VM appears as block-based DAS to the guest OS. The NFS datastore just has to be fast enough to avoid being a bottleneck to the Operations Manager database. Specifying a generous amount of cache for the database (dfm options set dbCacheSize=n) will help to reduce disk I/Os and improve performance.
From personal experience, I can tell you that you must guarantee the RAM for the Guest OS running Operations Manager. I constantly run into customers who have allocated the appropriate amount of RAM to the VM, but are having performance issues. This is because the RAM is configured as dynamic and usually isn't there when its needed. Once they guarantee the RAM, performance is immediately improved. I'd recommend guaranteeing the CPU as well.
Finally, SnapDrive 4.1 for UNIX is also supported in this configuration which would allow for LUNs to be mapped to the VM. The Operations Manager database could be installed on the LUN for optimal performance and snapshot backups. However it could make things like HA and Vmotion more complex.
The one DIS-advantage of running Operations Manager on a physical server is when you need HA functionality. You have to use host-based clustering which is much more complex and expensive than VMware HA.
