If his real mother is human as said in the story, and his father an orc, then he is a Half-Orc.
If Bhaal was his father, he would have his mother's appearance, and he would be Human.
Unless you imply that for some weird reason Bhaal decided to transform into an Orc and make her believe she was violated by an Orc. It's too forced to make Dorn a Bhaalspawn.
Comments
If his real mother is human as said in the story, and his father an orc, then he is a Half-Orc.
If Bhaal was his father, he would have his mother's appearance, and he would be Human.
Unless you imply that for some weird reason Bhaal decided to transform into an Orc and make her believe she was violated by an Orc. It's too forced to make Dorn a Bhaalspawn.
So in my opinion, he's just a Half-Orc.