LT tires in the US are not tested and certified for trailer use. If the government says they are not certified for trailer use, the company shouldn't recommend them
Do you have a credible link that shows the LT tires are not certified or tested per any government specs for trailer use.
Keep in mind here gov testing per the FMVSS's and dot certification cover all tires.
What the OP has done like most new folks when asking questions from a tire maker is he has backed them into the liability corner.
When dealing with a tire maker don't say you want to replace the ST tires on your trailer with a LT ....OR you want to replace the LT on your trailer with ST tires. You have backed the tire maker in the liability corner and they will give you the "no we don't recommend doing so" std answer.
Now if you ask the tire maker a question like "I have a 6500 lb trailer and would like to use your LT tires rated at 1760 lb each then you will get a different answer.
Now having said that when it comes to dealing with Maxxis on LT tires or ST or P tires issues I've noticed posters on different truck or trailer forums report Maxxis would not recommend replacing P tire with LT even on a 1/2 ton truck. So its not surprising what Maxxis would say about anything when it comes to tire selections.
I would simply tell my Maxxis dealer what I need and let him mount them.
There are other good 14" LT and Euro all position tires out here.
By the way those tire sizes listed for the Maxxis 14" U-168 are a Euro all wheel position sizes.