You cannot get back information that did not exist... Reading an AutoCAD hatch boundary and applying it to a Zone might work, but for Walls, Slabs and Roofs, there are too many variables that you would end up needing to check everything if you could get it to correctly determine what is what in the first place.
For Slabs and Roofs, if you merge the .dwg into the model, can you magic wand them if they are complicated? Right off the bat, you will get all your correct thicknesses, composites, angles, etc.
Ling.