For a stock z with stock parts, -4 degrees of rear camber is way out of spec. I would be concerned that you bent or damaged something for it to be that far off with all else being stock . If there is damage or a collision you will most likely need to replace suspension components. If you are lowered you will need a camber kit and to bolts to return the car to near factory settings.
If no collision or impact is present and you are stock height, yes, you should be able to get the rear back into spec by having the car aligned.