Arrrggghhh!! A direct quote from the link provided:
"Trailers will be more stable and pull better on tires designed specifically for trailer use. Since Special Trailer (ST) tires are constructed with heavier duty materials, they are tougher than typical passenger vehicle tires. This is a plus because trailer suspension systems are generally stiffer and less sophisticated than automotive suspension systems."
Have the people who write this drivel ever actually examined an ordinary cheap ST tire vs something like the Goodyear G614 or Sailun S637? The difference is like comparing tissue paper to Kevlar fabric. Just unbelievable.
If it were me and I didn't know anything about the Westlake "G" rated tire, I would talk to the dealer and see if something could be worked out to change to a known quantity, like the Goodyear and the Sailun. It can't hurt to ask, and really why take a chance with a brand new trailer?