I can't speak for all manufacturers and/or dealers, but it is almost certainly the same people, or at least the same process. During dealer prep they will definitely fix anything broken, or damage to the car that made it past the factory inspector or happened during transit. And they will install certain options that you can buy but are not done at the factory, including installing parts that are prone to being damaged during transport (for example, the spoiler on my GM car is not optional, supplied by the factory, and has to be installed by the dealer body shop after the car arrives).