You should be able to utilize the snapcreator command line to start the backup like you have described. I would try with only installing the agent. You wouldn't even need to run the agent as a service, as you are just interested in the CLI.
One thing I would point out is that you are potentially missing the ability to centralize your snapmanager schedules in SC. You have described:
- Run SMVI schedule and create backup
- SMVI post script to call SC
- SC grabs external snapshot and then registers in PM
- PM then vaults the snapshot
If you wanted to have a central scheduler, you could do something like:
- Run SC schedule which calls SMVI on remote host to create backup
- SC grabs external snapshot and then registers in PM **
- PM then vaults the snapshot **
** You could even skip PM and just have SC handle the vaulting.