I use ZBrush 2, so this may have been fixed since 1.55 - but my ZBrush doesn't crash when importing an OBJ with overlapping UV's, but it does make texture painting & exporting displacement maps impossible. Painting results in weird streaks in the texture (as the color from a stroke on one set of UV's is applied to another), and displacement mapping just dies. The problem I have mostly is that once you delete the eyelashes, etc from a head OBJ - it becomes impossible to import geometry back into Poser as a morph target (making it absolutely necessary to restore the original shape before exporting displacement maps). When making completely different characters from a base head shape (say an elderly british gentleman from Don), this can a real pain as one needs to create the basic shape in ZBrush, export it to Wings, remove the eyelash polygons & so on, reimport into ZBursh and then paint on the displacement maps... This is a real pain in the rear