Looking in the documentation here:
UrBackup - Server administration manual (Section 6.4.1)
I see that to back up e.g. a non VSS aware database one can stop the service in the prefile or preimage scripts, & restart it in the post backup/image scripts.
However, this represents a long interruption to whatever service or process is stopped, it would be very useful to restart them as soon as the VSS snapshot completes rather than waiting potentially hours for the entire backup to finish.