We did this with the XT. The issue is with creating a model with thermal only. Of course you cant have radiometric model, no software supports it so far. You can create a model of a building with thermal map, but you also have to fly RGB with the same flight path. It looks like this: you map an area with the X3/X5/X5R. Then you map the same area with the XT. Since the XT has such a low resolution, its nearly impossible to build a model out of it. So you create an RGB model, and than you put an XT texture on the same model. Correct me if I'm wrong but this is the only way so far.....
Are you using Pix4D in this workflow? If so, how are you layering the XT texture?