Since Sametime is not a VSS-aware aplication then there are two possible approaches:
If a crash-consistent backup of a VM is enough then you can perform simple backups without any extra precautions. However, if you need a transaction-consistent backup then you'll have to utilize some scripts
in order to put your software in a backup-ready state. Also please take a look at this video
- though not about Sametime but still might be useful.