Having had a harley and been part of that culture in the past, personally I can attest that the cultures are almost IDENTICAL. Oh there are a few minor things that are a little different, but those things are pretty much interchangable. About the only thing I don't see the Ducati riders do is have poker runs.
I bought my M800 cause it looked like it would be a blast to ride, just like my old sportster was (and so far this has proven to be true), and it's highly customizable. I'm already planning a bunch of mods to the bike to make it more like I want it (like getting rid of the udder, better seat, tail chop, hugger, etc). I think Ducati's are very much like Harley's and in many ways so are the riders (And both groups have had a large influx of yuppies!
I don't buy my bikes because of what I think other people will think or will like. I buy them because -I- ride them! I am a motorcycle enthusiast, and if I was rich, I'd have more motorcycles than Jay Leno! Whether or not Ducati and Harley do any sort of a deal remains to be seen, but I don't think it would hurt either company, and hopefully it would increase the accessories market.