Actually I have to disagree with William. The VMware Snapshots only value is the VSS writer inside the Guest that makes an attempt at quiecing the file system as William described. However all modern OSes use a Journaled filesystem and very rarely is their any data sitting in the VM guest SCSI driver. IO normally flows from the guest SCSI driver and immediately into the vKernel IO stack. Therefore, in my opinion, the guest quiecing option provides little value in the way of consistency. Moreover the VMware snapshot process tends to be disruptive to the guest and can often lead to trapped or orphaned VMware snapshots. Again, in my opinion, you are placing the VM at greater risk by using this option than the risk of data loss of not using it. That is, I believe the odds of an outage of the VM or data loss in the VM due to using VMware snapshots is greater than the odds of data not being consistent during a NetApp snapshot. Moreover you can further improve these odds by taking more NetApp backups(snapshots) if you are not using the VMware snapshots.
I would save the VMware snapshot option strictly for certain VMs that perhaps need some sort of guest OS flush (not sure what those workloads would be though).
Unfortunately neither NetApp, nor VMware, nor Microsoft have an official stance on this so you are left to make the decsion on your own and listen to the advice (for whats it's worth) from folks like William and I.
Keith