I had an Invidia Gemini exhaust on my 370Z and I don't recall it hanging significantly lower than the stock exhaust. Here's a picture showing the lowest point, which is at the rear-most joint which is just behind the rear diff.
My car was lowered by 0.75" in the front and 0.5" in the rear. Didn't have any problem with scraping. I haven't heard of other Gemini owners report of rubbing either, unlike some FI exhaust owners with lowered cars.