I would apply the modifiers if I were to export a model, but I rarely work outside of Blender these days, so I’m not exactly sure. I do remember JL doing the UV Smooth setting on a couple of tutorials, in the SubD modifier, under advance. Maybe that helps you.
JL explain UV stretching and other facts on this lesson:
https://cgcookie.mavenseed.com/lessons/fixing-uv-skewing-and-stretching

