The file is the same if the full path, having resolved all symlinks, is the same, the file contents are the same and the files timestamp is the same.
Symlinks are backed up as symlinks, so to full resolve a filename including symlinks, you need to not backup these symlinks and told Bacula to do so (a special preparation of the fileset).
If you need to check a contents of the file before backup, then you will read a file twice. You can resolve this using base jobs.
