I just found today that Hyper-V snapshots are recommended by Microsoft only for development and testing purposes. You should never try to use Hyper-V snapshots instead of fully functional backup solution!
There is even more on the Hyper-V Virtual Machine Snapshots FAQ:
Microsoft does not support the use of snapshots on virtual machines hosting the Active Directory Domain Services role (also known as “domain controllers”) or virtual machines hosting the Active Directory Lightweight Directory Services role. For more information, see Operational Considerations for Virtualized Domain Controllers (http://go.microsoft.com/fwlink/?LinkId=159631).
There are many horror stories in the net about losing all production environment due to Hyper-V snapshots failures. Snapshots are also based on differentiating disks so it will hurt your performance too.
Here are some pros and cons about Hyper-V vs. VSS backups.
VSS stands for Volume Shadow Copy Service and it is used by Windows Server Backup available in Windows Server 2008.
There is also some known way to enable Hyper-V VSS Writer as it is not enabled by default.