He is only mentioned twice in the game; the first is to Alan when Hartman tells him Jack has taken other clinic patients on a fishing trip. The second time is in the manuscript page titled "Harman Watches Wake Fall", where he was on the boat that saved Alan in Episode 3: Ransom.
Hartman Watches Wake Fall
"Hartman followed the fall of Alan Wake with his binoculars. When the writer hit the water, he ordered Jack to take the boat to him.
The spot was easy to see in the dark even with all the extra lights in the boat. The flare floated and kept burning even in the water.
Jack turned the radio louder as the engine sputtered. The music was rough and clanking, something the Anderson brothers would no doubt have enjoyed, but Hartman chose to ignore it. Wake was finally within his reach."