If the setup requires you to have certain zombies in locked rooms from the start, when you open the door to that room do you still draw a card to add even more zombies to that room on top of what setup told you to put in it? (Example being the tutorial quest 0 where it has a fatty in a locked room alone, when you open the door to him do you spawn more?)
Yes, because the spawned zombies represent the unknown ones being revealed, e.g. the ones hiding under the bed!
Opening a closed building for the first time reveals all the Zombies inside all rooms of the building
Source: Page 20 of the rulebook. Emphasis is mine.