Sounds pretty good. But they released the hashes, they could just replay them. You could release the files with those hashes, but that's illegal. You could send those files to f0f to verify, since f0f is trusted, and it's still illegal but files aren't getting released so that's a plus.
There's Wii U system files that f0f hasn't released information about, but are known by f0f internally.
These hackers can hash all the Wii U system files and release those hashes. If those hashes match f0f's hashes, then this is probably real as it demonstrates that the hackers have Wii U filesystem access capabilities that aren't public at this time.
Of course, this still needs a bit of cooperation. Just a bit.