Sorry for the french. So i speak in bad English
I've tried integration of Maya file in Terragen, and it's seems to work.
For the moment your object must have less than 16 textures.
here is some tests that i've made with Maya imported objects.
A simple object with 1 texture file.
A more complexe object (more than 16 textures)
And in that scene some faces don't appear, maybe because I've made a mirror of the truck, but in Terragen the texture is in 2 side.