We use a combination of stock textures and some custom ones that still mesh well together, so this may be why some textures may appear lower res.
The Black Parade isn't compatible with graphics mods. The campaign was not designed with any of them in mind. You can still use them if you want but you'd have to do it manually.
It's a very interesting mission because it really, really looks like a lost mission from Calendra's Legacy, using mostly the same texture selection, similar sounds and built very similarly to both A Meeting With Basso and Midnight in Murkbell. I think it's a fantastic mission and it's crazy the author tried to make it under Olddark when you consider the sheer scope of it.