Snapmirror allows replication of a volume to an exact copy located on the same controller or a remote controller. This is typically used for DR or recovery.
SMVI is a snapmanager product that allows you to take quiesced snapshots of one or more datastores and/or VMs in your VMWare environment (usually) for the purposes of backup. You can use it to take point-in-time snapshot backups of your environment, and also restore individual .vmdks, VMs, or entire datastores to those points in time.
Both can work together too. You can use SMVI to take local backups, and then use Snapmirror to replicate on every snapshot so you always have a fresh copy of your VMWare environment on your remote controller (perhaps located at a DR facility). SMVI even has a checkbox you can check when setting up the backup schedule to automatically replicate to your SM destination on every backup.
Also, don't download the SMVI 2.0 client. Download the Virtual Storage Console instead. The former has been deprecated and replaced by the latter.