Umm, i think you mean his biological FATHER
It's a good theory. But if true, it'd be very revisionist. The kid in the photo has played young shawn in the series - obviously - and if he knew that was his mother, you'd think it would've worked it's way into the show by now if that was part of his background all along.
Also if true, he's got some effed up biological parents. Pair of killers? Yikes.
The episode where Yang tried to kill his mother is like 2 years old, so i can't recall if they explained any connection between them or not. I'd like to know why there's a picture of her with young shawn.