You cannot use SAN access protocols to access FlexCache volumes. You can cache a volume that contains LUNs along with other data, but this configuration can change system behavior.
When you attempt to access, in a FlexCache volume, a directory that contains a LUN file, the command sometimes returns "stale NFS file handle" for the LUN file. If you get that error message, repeat the command.
If you use the fstat command on a LUN file, fstat always indicates that the file is not cached. This is expected behavior.