VSS Backup Writer Not Being Included

I develop a database backed business software solution. Our database provider has recently provided us with a VSS writer that is capable of flushing our database during VSS aware backups. Acronis is not invoking our VSS writer even though the writer is installed and registered (under 'vssadmin list writers').

I don't currently have a volume that is appropriate for a volume-wide backup (not enough backup disk space), so I am using a file-by-file backup task. The backup runs, and OnIdentify is called in the VSS writer. But no subsequent calls are made to 'OnPrepareSnapShot' or 'OnFreeze', so our database and files are not flushed and could be inconsistent in the backup.

Does Acronis limit its VSS writers to a specific list (like 'exchange', 'sql', etc.)? Or is it possible that the file-by-file backup is not specifying sufficient information to load our VSS writer?

I am only evaluating the Acronis compatibility with Microsoft VSS, so I am using an evaluation version of Acronis, and it doesn't seem like Acronis supports all of the VSS infrastructure.