If you render a viewport in just Hidden Line, does it appear as expected?
If so, you can layer a hidden line viewport over your original viewport, giving it no fill, which should emulate the same appearance as the background/foreground viewport, as a workaround.
However, please send the file where that is happening along with this from your Mac Pro:
http://kbase.vectorworks.net/questions/627/DirectX+Diagnostics+and+System+Profiler
to tech@vectorworks.net and we can have a look.