Tire Rack is also at the mercy of whether or not the manufacturer will warranty the tire. I see this all the time at the shop where I write service. I install an A/C compressor, the customer comes back and says it doesn't work. My tech tests it and finds that the compressor is faulty. Now I'm stuck in the middle and so is the supplier. I have to prove (on the phone) that the compressor is faulty, AND do so with enough conviction and evidence that the supplier feels confident that the manufacturer will warranty the part once I send it back.
Tire Rack will obviously be trepidatious at first and look for possible reasons to not have to warranty a tire. If they just roll over and give you a new tire and the manufacturer doesn't reimburse money, Tire Rack would be constantly giving out free tires.
I must add that my Uncle works for Tire Rack and I'm not blindly defending them, I'm merely giving you a counterpoint. A full 65% of their business is custom fitments. Many times they sell a custom wheel/tire combo to someone who insists that it will fit their car, it ends up not fitting, and both the wheel AND tire manufacturer won't accept returns on parts that have been mounted. Its logical for them to be even MORE selective on warranty repairs than the manufacturer. If they weren't, they would be footing the bill for millions of dollars in replacement tires that the manufacturer didn't cover. Keep in mind that Tire Rack is the middle man. They can't make money if they're making snap decisions to replace a race-type tire used in a non-street application just because the customer says it failed during normal use.
Its much like my job. I have a repair right now where the customer ordered a new window regulator for their civic and found they were in over their head. We opened the package to install it only to find that the regulator is the wrong part. Honda won't take the part back, the customer thinks its our responsibility, and I'm stuck in the middle trying to resolve it.
I don't mean to belittle your loss, but seriously... you're using a race type tire on a race track for the purpose of training drivers in non-street situations... or at the very least, constantly simulating the worst possible street maneuvers. That is hardly normal wear and tear.
Manufacturers warranty street tires because 90% of them are used in a predictable street manner. The 10% of idiot teenagers who try to race on touring tires doesn't affect their bottom line. Race tires don't typically get warrantied because they are subjected to all kinds of abuse. True, your DE event doesn't necessarily mean that you abused tires, but there is no way that Tire Rack can trust a customer's word. If Tire Rack sends back a tire to Dunlop and says (basically) "this tire was used in a track event, but it wasn't raced, and this outside front tire got damaged," guess who pays the bill to warranty your tire... Tire Rack.
That's kinda like if you sued the 7-11 for selling you the pack of Marlboros that caused your cancer. Don't blame the middle man. This boils down to something between you (and your use of the tire) and the manufacturer.