There is a difference between the statement recorded under sec. 162 and sec. 164. Statement under the provisions of sec. 162 is recorded by the police as a matter of preliminary investigation in to the case before filing charge sheet in the court of law, while statement u/s 164 is recorded by the Metropolitan Magistrate or Judicial Magistrate as a confession of a person (may or may not be during the course of trial), but like an examination-in-chief to be used in the course of a trial. While statement u/s 162 is not signed, statement u/s 164 is signed by the person making statement. Statement u/ 162 cannot be relied until proved beyond doubt, while a confession made u/s 164 has to be relied as is made before a Metropolitan Magistrate or Judicial Magistrate.
Statement u/s 162 cannot be shown to the concerned person for corroborating his statement, except to be used for contradicting his earlier unsigned statement given to the police. Otherwise Corroboration of the earlier statement recorded by the police would mean putting the words of the police in to the mouth of the witness.
So, as I stated earlier, the statement u/s 164 being a confession statement and recorded before a Metropolitan Magistrate or Judicial Magistrate can be relied and hence can also be used for corroboration. However, that statement can also be subject to cross-examination for the purpose of contradicting that based on some vital evidence against that statement, as the same is used as examination, not cross-examination.