I am an attorney in CT, not NY, but I practice criminal defense and civil litigation.  The rules in court as far as witnesses are generally the same in all states as most state rules are based on the federal rules that we all follow.  Regardless of whether you are following the state or federal rules, both permit the accused to bring in any witness they want to support their defense.  Indeed, the US Constitution would be violated if the defendant was precluded from bringing in a witness such as the one you describe here.  Once the witness is on the stand, the issue will be whether they have personal knowledge about the subject matter and whether certain testimony they elicit is admissible (i.e. hearsay, privileged, etc.).  So, the answer to your q is yes, the accused can bring in the witness.