Thank you for your post.
FileMaker is not VSS aware. You may want to schedule backups overnight when there is no activity.
I suggest you enter this into our Feature Requests web form at:
These web form suggestions are monitored and read by our Development and Product Management departments where they are then discussed and considered for a future release. Although I could copy your post and paste it into the web form, there are some questions asked that only you can answer.