I don't know, but most probably one would see some z-fighting.

Just another thought, because of something you mentioned:
Is it possible that one uses two identical models, both as almost huge as the level seems to be, and then render the textures with alpha channel of one of them always in front of the other? F.i. one model with the rocks and a second with the sand and scratches on it.

That wouldn't be a solution that is very easy to use, but it would be a beginning...