When I was shop foreman, I interfaced with the field engineers quite frequently.
I found that GM talked a hard line, and posted a great deal of information on aftermarket power adders and accessories. there is also a sales department that wants to sell vehicles. there are a lot of Dealer techs that will do anything to get out of warranty work, or even standing behind any work they do. I did not care for them. when it all came down to it, the aftermarket equipment has to be proven to cause the failure in order to deny warranty. We had a truck catch fire, it had led lights under it, wires scotchlocked into connectors for a programmer, and every other aftermarket device that was popular in 2003! There was also a bulletin on a driveshaft being an inch too short. the truck was totaled and the manufacturer paid the entire truck off and gave him a trade in certificate. I had to fight with them a bum but the field engineer agreed, the shorter driveshaft made the trans leak fluid onto hot exhaust and catch fire. Truck was so burnt it was hard to tell.
The biggest telltale on an lml ecm or even the new ford and dodge is the maximum desired torque number that is stored and can't be reset. That is the number they will look at and they know it can not be tampered with. So there is no reason to turn a guy in for having been deleted.
Lets look at like this. You just are deleted no increased power, or maybe 50 hp tune.
there is a huge emmisions system that they no longer have to warranty. they put it on and they did not take it off.
Now lets say your engine drops a valve or bends a rod. They can go in and look at max desired torque. If it is within stock limit than the engine failed under stock like power. why not warranty it. If the max torque is higher than allowed than you turned it up and they can look at what the cause was. If the rod bent because the head gasket failed because it was an early design (known problem) head gasket and the engine hydralocked, well that could still be warranty even though you have 2 turbo's on the thing and a dual fueler.
I hope that is helpful