Server 2008 Sp2 Enterprise fully patched
Two Exchange 2010 DAG fully patched
The Windows Server Backup feature was installed with command line tools. I uninstalled the command line tools later after reading that they break the Windows Backup Server plugin for Exchange on technet. The plugin's service is set to automatic and started.
The registry is modified to disable VSS Writer as recommended on technet, although I don't think the server ever has active and passive copies of the DAG at the same time.
The backup completes, but with this error: "Application will not be available for recovery from this backup. Consistancy checked failed for component Microsoft Exchange."
The logs do not truncate.