Yes. It is not just a get-away vehicle; it is a portable shooting platform, concealment device. Shooting from inside the back of the vehicle through a custom opening in the rear door, the shooter is not seen; the only exposure to being seen is to the witness who is looking at your door at the moment of firing--otherwise the van holds much of the noise and no one is likely to see the shot. You close the window cover immediately after the shot and drive off like you are part of traffic.
Again, the advantage is that for the most part, your truck is not likely to be identified as part of the action. The business sign on the side makes you part of the normal commercial traffic. If it is identified, you repaint it yellow and put a Ryder sign on the side; or paint it brown and put a UPS lable on the side; or whatever.
The White Isuzu would be a great choice because they are all over. You shoot out of the back, close your window and you have a good chance of being right next to an identical vehicle in DC traffic.
Not to say that the box van is really part of the operation, it may be only the Chevy Van or a pickup or some other unidentified truck.
The box van has another advantage--not only is it a complete comfortable shooting platform but in addition, you could mount a RPG launcher, and a couple of 50's, and maybe a couple of other personel with field weapons in the back--so if the authorities identified you, you could roll up the back door and have a good chance of having enough more firepower than your pursuers to fight your way out.
I'll bet for every Isuzu parcel delivery truck on the road there are 100 Ford or Chevy minivans. The truck would stand out in traffic like a sore thumb compared to these minivans. Second, putting lettering on the van only aids in identification. Think, the shooter takes a shot but this time a witness see the shooter in a large white truch with Fred's Market (or some similar logo) on the panel and calls the police. This truck could very well be spotted long before the shooter could repaint it. It isn't intelligent to put a large identifing tag on our get-away vehicle.
Your comment about the RPG laucher seems pretty far fetched. For one, this shooter is a coward. He runs from his hits an is unlikely to engage the Police in a shoot-out when the finally find him. Plus, if you have a RPG launcher mounted, why not use it for yoy initial shot as opposes to a .223. It would sure make a bigger statement.