No, the "fashtag" is a great example. The trolls are trying to exploit paranoia about dogwhistles. Their goal is not to make fascists use the hashtag, but to laugh at (hypothetical) people who avoid hashtags because of internet hearsay that it might be a secret nazi symbol.
It takes two to tango - this particular kind of trolling doesn't work (and didn't work in the case of the fashtag) when we relax a little about dogwhistles. I won't let them take away my feelsbadman.jpg.