In creating a backup, there may be an issue with the lock file, or with an inuse journal file. The lock file is not important but you would want the latest journal files.
Batch writes are serialised and followed by an fsync, so the fsfreeze will either block the next write or the next fsync. Either way is fine from a consistency point of view. The index is checkpointed to the journal periodically, so recovery of the index will at worst be from the last know good state.