Jake got Zack killed in more ways than one.
First he got him kidnapped because of the drug debt and all the back and forward between the two. Secondly, after talking to Frankie about killing Zack and Frankie talks him into greasing the kid instead, Johnny was actually going to send him home. In the next scene, we see Johnny calling Jake from a payphone and Jake goes berserk, threatening Truelove about Zack's disappearance. The whole purpose of Truelove calling Jake was to find out how much the family knew and if he was already suspected of the kidnapping. If Jake hadn't mentioned the kidnapping or at least not imply that Truelove was a prime suspect and threatening Truelove then most likely they would have sent him home.
I woke up this way...