Well, you'll need some kind of heuristic to figure out if a mismatch is due to bit-rot, or because the working file's changed. Maybe modification date, but a) what if a file's restored from an older backup, b) mtime itself is corrupted (APFS would guard against this I suppose).

In any case, the "hash" appears to be CRC32, stored in extended attributes:

  $ xattr .inputrc
  com.apple.finder.copy.source.checksum#N
  com.apple.metadata:_kTimeMachineNewestSnapshot
  com.apple.metadata:_kTimeMachineOldestSnapshot
  $ xattr -px 'com.apple.finder.copy.source.checksum#N' .inputrc
  26 E5 4A AB
  $ cksum .inputrc
  2873812262 65 .inputrc
  $ printf '%x\n' "$(cksum .inputrc | cut -d ' ' -f 1)"
  ab4ae526