I'd be willing to bet there are no tire manufacturers recommending LT tires over ST tires for trailer applications. Legally speaking, makes no sense for them to do so.
legally speaking you would lose that bet.
You must be a new guy to the trailer towing world. I was a new guy also....many years ago.
Before the tire makers came up with a ST tire OEM tires on our trailers were light truck and passenger car tires.
And before the net RV trailers came OEM with LT tires
I have Emails from Michelin/BFG/Cooper/Goodyear/Bridgestone all recommending a particular line of LT tires for trailer use and we get a full mfg warranty just like we always have.
There are no legal issues/no vehicle code violations regarding using a P or LT on a trailer as long as it meets or exceeds the trailers axles ratings or the trailers registered gross weight if a state enforces such.