Do we know what they modified on the vehicle? As has been pointed out, there is a big difference between stripping a production vehicle, and a manufacturer (that has full access to the vehicle) modifying a vehicle for a specific event.
How much of the hardware and software did they modify from "production intent?" Seems to me that they had the opportunity to tune the car to a degree that is unavailable to owners of production BEVs (well at least Teslas).
The White Zombie EV is a perfectly good example of what you can do with a vehicle if you have complete control over all the systems, and the ability to tune it for a specific activity.
It was certainly up to Tesla whether to provide tech support to the Tesla privateer or not. I doubt the team failed to contact Tesla and request support.
When we set a land speed record with a GMC truck, prior to the attempt, GM agreed to provide me with tech support (custom transmission flashes), but they chickened out a month before the event for fear the coding would somehow get out into 'the wild'. This is why you won't see GMC or GM banner on our entry. A few years later, Ford Motorsports supported a team to break my privateer record by 3 mph. That's probably the most expensive 3 mph Ford ever bought, and they still didn't come close to matching my top unofficial (only 1 pass) speed.
What would it have cost Tesla to release the programming tools or custom flashes? A few thousand at most. But motorsports are a slippery slope. What image are you trying to project? What's the brand reputation cost if you lose or break? Can you justify the budget to win, and will it reap a profit in increased sales?
Faraday has little to lose at this point. A factory entry at a race event gives the image of a viable company, something Tesla does not have to prove anymore. Tesla has marketed themselves to the press as the world's fastest sedan, and other superlatives, so losing to Tesla proves nothing but participation. A DNF would have hurt Faraday, but they did finish. Only Faraday will be able to answer whether the entry was a good bang-for-the-buck, but I'm guessing it will help.
Tesla has nothing to prove, and everything to lose. And they have some potential high rollers to compete with. At some point a major automaker is going to try and prove a point.