Continuity mistake: When Shanda is sat on Debra's desk, her handbag keeps moving from on her lap to at her side between shots.
Revealing mistake: When Valerie's dead body is on the table after being brought up from the ocen by the ice truck killer her nipples are hard. If she was dead her nipples would not have any reaction to the cold.
Answer: No, Harry is not the real father. While he did have an affair with Dexter's biological mother (Laura Moser), this was when she was his C.I. Dexter was already born at that point.