Big Waylon, please correct me if I'm off base with any of this...
I think it's important to keep in mind that major silencer manufacturers can and have "done things" that you and I might run into ATF trouble with.
My read is that any structural part of a suppressor is a "suppressor part." It may or may not hold baffles in, but there's some sort of necessary function to that part, making it somehow special to that suppressor.
The whole point of the flash hider/silencer mount is not (necessarily) to allow you to use the silencer on multiple firearms, but to allow you to remove the silencer from that particular firearm. Gemtech, AAC, YHM, and other brands of silencer mounts are essentially the same thing as the thread adapter I mentioned in my earlier post. The part that the mount fits in the suppressor is a suppressor part (whether it holds in baffles or just whistles "Dixie") and you can only have one of these per suppressor, while the XYZ suppressor mount is unregulated.