No, you don't have to be registered for ZendCon to attend the H2.0 (that's sort of the point :-)), however the evening stuff will be open to all attendies of H2.0 including the exhibit hall. I imagine a lot of the speakers will be there also.
I don't know about free parking, but the hotel parking is $3 (free with validation) and there is a shuttle from the SFO BART to the hotel. :-)