Are Bioimpedance sensor different from Biopotentials sensors?
A biopotential sensor is simply a voltage meter with skin-compatible electrodes. A bioimpedance sensor is an ohmmeter, typically an AC ohmmeter. That's all there's to it. You've already listed the applications: measurement of ECG, galvanic skin response, EKG, EEG, EOG, etc.

Usually an impedance meter already has a voltage meter built-in, so any bioimpedance sensor can be easily made to sense the open circuit voltage when the excitation current is turned off.