It is actually not confirmed that it is Gratteri that is speaking with NCG. Plus, it is not a given at all that NCG knows anything about Germany and of course if he says something German police is bound to talk to him.

Buscetta was a low level criminal compared to NCG, the parallel is ridiculous - it's just that they are two different criminal organisations so Buscetta could know a lot more because of that. The 'ndrangheta's first pentito, Pino Scriva was the first Buscetta maybe. Bah.