Well, when I replaced my clutch at 100k miles the DMFW definitely needed to be replaced. It was pretty roasted.
So I decided to save some money and install a lightly used one. I would have preferred using a new one because I had no way of verifying the condition of the dual mass mechanism. It can wear out and cause chatter, noises, or rough engagement. Obviously I got away with it and I think you probably will too. The problem is that if the flywheel goes bad you have to drop the whole trans and do it all again. You decide if the risk is worth it for you.