SnapManager is for application backup support... SQL, Oracle, Exchange, VMware, SAP, HyperV, etc.
SnapDrive is Lun provisioning (an exception with smo and oracle over nfs) and quiesceng of file systems. The windows version handles Snapshots to ontap, provisioning...and more
Snapmanager products use snapdrive. They work together.
I would get on one of the weekly demos or get a lab on demand demo. Also there are video demos (YouTube NetApp channel) and product data sheets give better explanations that I gave
