I see biometrics can be used as a source of entropy/seed while generating keys. However, it should never be deterministic. It just too "fuzzy" for that.

Most of biometrics does not produce fixed data blob every time you run it, instead recognition system "trained' and produces probabilistic classifier (Sift, HAAR, AAM/ASM in computer vision/face recognition). Classifier being applied to your blob generated by biometrics tells you probability - like 0.87. You set the threshold what should be considered "true" and what "false".