No its not synergistic with the natural man cooperating with God, but after its given in regeneration, the new man born of the Spirit is caused to repent Ezk 36:27-28
26 A new heart also will I give you, and a new spirit will I put within you: and I will take away the stony heart out of your flesh, and I will give you an heart of flesh.
27 And I will put my spirit within you, and cause you to walk in my statutes, and ye shall keep my judgments, and do them.
Now its synergistic with the ones a new heart has been given, a new spirit is in them, they no longer walk according to the flesh, and they are caused to repent, its in agreement with the new heart and life given in regeneration.
So its the new mans part in the act of repentance Eph 4:24
And that ye put on the new man, which after God is created in righteousness and true holiness.
Now we agree if you mean the New Man created in righteousness has part in the synergistic act of repentance.