This person on EBay says they are forged, people on EBay rarely lie, so they must be!!!

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=8002499401

Does it really matter? Either use them as they are, or sell them. From what I gather on Google, VW tuners pay big bucks for these rare wheels.

If you could get the weight of a Fuch the same size and then get the weight of yours... A more simplified version of Souk's density test which is probably the best way that wouldn't involve a destructive or invasive test.

WOW! Since it's listed on E-Bay they must be forged:) . And since they arfe soooo rare I could probably trade one of my fronts for an entire set of 8&9 X 16 Fuchs.:D This is truly great news.

If they were forged wouldn't they resonate at a higher frequency if struck with a metal object? You would have to remove the tire and it would be a subjective test at best, but I've heard this method used to evaluate the density of tool steel - i.e. the more of a 'ping' sound the higher the density; the more of a 'clang' sound, the lower the density.
Or as another poster pointed out, you could just reach for your handy electron microscope and examine the molecular structure. I'd say forged as a default - who would admit to cast wheels?