[Baja Guy]

I'm a tire guy, have sold & serviced them since the 80's.
Here are a couple of things you can be assured of. Tires should come out of service after 6 years. If they haven't worn or cracked by then they will likely separate internally under load after that time. If they are tremendously over capable they may work longer, but loaded normally which is from 75 to 100% of rated weight, they won't stay together much after 6 years. If they do it's only a matter of time.
This is especially true of trailer tires on travel trailers because the cheapskates at the trailer companies put on the absolute minimum tire for the job. It can be true on boats too, so learn the loaded weight of your boat & trailer & make sure you have correct tires for the job.
To answer your original question, manufacturers will warranty defects that are listed in their warranty. But it doesn't occur very often. Rot is hard to get on a claim, it's better to look for big cracks, read separation or air loss. Normally those items are listed as having a 6 year limit!