SAE J1772 has a data pin, yes. It's how the car communicates rate-of-charge.

The Supercharger uses a different plug, though, which I don't know anything about. The voltage (440v) and speed indicate DC charging, which J1772 doesn't support. (The Leaf uses the CHAdeMO connector for DC charging)

Yes, the Tesla charging port has a data link that allows Superchargers to speak directly to the battery's firmware. There is almost certainly "Tesla DRM" built into the handshake between the S and the Supercharger, although like all DRM it could probably be reversed engineered and compatible systems created. That's a lot of fun when you are trying to copy a Blu-Ray, less fun when you are dealing with 100kW.

In a standard charger, the car has to negotiate a power level before there is any voltage on the charging pins at all. http://en.wikipedia.org/wiki/J1772#Signaling However while the Model S comes with a J1772 adapter, I'm sure your Leaf doesn't have a "Tesla" adapter.