The other fingerprint system would need to be compatible with your data source, but if you had a compatible system and if you could generate every potential fin

The other fingerprint system would need to be compatible with your data source, but if you had a compatible system and if you could generate every potential fingerprint for a given hash you could definitely use cross-checking to find any individual in your several million who also happens to be in the database. I think the biggest potential problem with that approach is both incompatibility and also false-positives. You might have "too many" matches for it to be useful for much.