Well, this is from my friends and not direct experience. If the 911 call indicates a shooting and no further information is available, then the paramedics/EMTs will wait a block or so away until the police show up to secure the scene. Yes, this means the victim is lying there untreated for a few minutes, but dead rescuers don't help anyone.
On the other hand, as long as the paramedics get to the patient while he's still alive, then there's a very good chance the patient will make it into surgery. The key is getting the patient into surgery within an hour of the injury - long term survival rates drop way down if that doesn't happen. This is why medical helicopters are so useful, especially in rural areas.
With gunshot wounds, the biggest problem is blood loss. The bleeding needs to be stopped and circulatory volume made up, so that there's fluid to pump and carry oxygen until the surgeons can close the wounds to the circulatory system.