clarification on LT vs ST tires please

I just purchased a 2013 raptor toyhauler. I have been reading all the posts about tires along with all the either good information here. Here is my question: the toy hauler I bought comes with ST tires. They are made by General.

General doesn't make a special trailer tire (ST) or at least one doesn't show up on any of their web adds. They do have a General Grabber ST but its a light truck tire (LT).

But when I asked about replacing the ST tires with LT three, I was told that it would void the warranty. The keystone rep told me that LT were made for the two vehicle, not for a trailer. He said that's why STs are called Special Trailering tires they are made specific for trailers. Is someone blowing smoke up my skirt?

Yeah, lots of funny smelly smoke.
However not knowing the specific tire sizes and load ranges discussed were guessing here.

A ST235/80-16 E has 3500 lbs of capacity and works on 7k axles.

A LT235/85-16 E has 3042 lbs of capacity so yes using these tires on 7k axles will most likely void some kind of warranty. If you have 7k axles the Goodyear G614 or the Sailun S637 both at 3750 lb and a load range G works.
If you have 6k axles the LT E at 3042 lbs has always worked great.

A trailer owners only responsibility when choosing and installing a tire on the trailer is it shall meet or exceed the vehicles axle ratings.

The ST and LT both have the same number of plies in the tire. Both have a two ply carcass with two additional steel belts under the tread.

The exception is the commercial grade Michelin XPS Rib and the Bridgestone Duravis R-250 and M895 which have a one steel ply carcass with two steel belts under the tread. Michelin says the XPS ribs are recommended for commercial trailer service. Something "NO" ST tire can or has ever recommended.

A ST is for a trailer only but the LT can and has always been used in a drive/steer and trailer position.