Edit: Tesla Ranger service is not covered under warranty?
Well, I think the service plan and the warranty are two separate things. As far as I can tell, there aren't any details on teslamotors.com about what exactly is covered under the two warranties you get when you buy the car (there's a battery warranty and an everything-else warranty).
Annual service clearly covers things that are not under warranty, such as inspection labor, brake pads, wipers, etc. So that costs you at least $475 or $600 a year. That's if you take your car to a service center. In addition to that, if you choose (or otherwise have to use) the Tesla ranger service, you will also have to pay $100 per visit (unless you get that certain prepaid plan).
The way I see it, those charges are definitely for service that is not covered by the warranty.
I don't think there's anything on the website that definitively says one way or another whether or not you would be charged for the ranger service if necessary for a service job that is covered under warranty.
I would hope and expect that you are not charged. As a hypothetical example, let's say one of the belt buckle fasteners doesn't work and needs to be replaced, and let's assume that it's covered under the warranty (ie, it's a defect, not damaged somehow through misuse). I would expect that if feasible, that Tesla would ask you to drive the car to a service center and the buckle will be replaced for free. However, let's say you're 300 miles away from a service center. In this case, I would expect the ranger service to be free.
Now let's give a different example. Suppose you're an idiot, and you're racing around you're neighborhood at 100 mph. You go up a square curb and you actually crack a wheel! Now you need a wheel replacement. You can't drive to the service center, and so you opt for ranger service to get the wheel replaced. In this case, I would of course, expect you to be charged for the wheel and an additional $100 for the ranger service.