if you select None - you will have no application consistent snapshot, the snapshot taken on the array will be crash-consistent. Therefore if you restored from them you may need to perform a checkdisk or conssitency check (in the same way if you switched off your Server and turned it back on then you may see a check disk during the boot process).
Microsoft VSS is used when you are provisioning directly into the Windows server (via the Software initiator) and you wish to backup Exchange or SQL consistently using the VSS framework. In order for this to work correctly you will need to install NPM (Nimble Protection Manager) on the Host/Guest.
The VMWare synchronisation uses the vCenter credentials and uses the VMTools and VMWare snasphot in order to gain consistancy of the guests OS's. If the snapshots are being left behind (VMWare level or storage level - orphaned snapshots) that this could be a problem (usually it's race condition with another application taking a backup/VMWare snapshot at the same time) so it should be investigated