I configured my first WFC servers a few weeks back, having previously been at an all Veritas Cluster Server shop. Nothing particularly special about them, in fact 2 of the clusters are just 2 node clusters with an IP resource acting as a VIP.
We came to configuring backups this week, and the day after the backup had run on one of the cluster nodes, I noticed that the resource had failed over to the second node in the cluster.
Digging into the eventlog showed a large number of NTFS warnings (eventIds 50, 98, 140), as well as errors for FailoverClustering (eventIds 1069, 1177, 1564) and Service Control Manager (eventIds 7024, 7031, 7036).
A bit of digging into KB articles such as KB1037959 reveals that snapshotting is not supported with WFC.
However, the issue seems to be caused by quiescing the VM and capturing the memory state with the snapshot. Just snapshotting the disk state does not appear to cause any issues with NTFS or Clustering in our testing, but obviously this is just a crash-consistent backup.