Hi,
There is nothing built into the Sync Framework to enable it to run as a service to detect changes in files. That is not to say that you could not create a service and embed the sync framework functionality into that service to detect the changes.
Have you by any chance taken a look at the file sync whitepaper "Introducing Microsoft Sync Framework: Sync Services for File Systems"? In it, it discusses a number of topics including Detecting Changes on the File System which I think may be helpful to you.
Liam