When someone can even make charlie Batch look good ( Batch's 88.3 passer rating ranks as the fourth-highest rookie mark in NFL history.), then I would have to imagine that they are doing something right.
Not to mention, Haselback has praised Zorn's out of the box drills in the past. But your right, im sure Jim had nothing to do with Hasselbacks success. In Zorns first year as QB coach in seattle, he helped develop Hassellback into a pro type QB. He led the NFC in pass completlion, and was 3rd in the NFC in QB rating. This helped lead the seahawks to the third best passing attack in the NFL that year.
As for coaches going straight from QB coach to head coach, Andy Reid can tell you about it. Also coming from the Mike Holmgren coaching tree, Reid went straight from being a QB coach to coaching the eagles. Since being in philly, he has gained coach of the year twice, has a .608 winning percentage, has won 5 division titles and has reached the NFC championship game 4 times. In a nice year tenure, i'd say thats pretty good.