House Without A Key
There is a promenade from the Hilton that passes the HWAK, but I'm not sure that there is an actual entrance. If there is not, you can backtrack a little and get to Ena Road by cutting through the commercial arcade in the hotel next door, which I believe is the Reef. The arcade does have access from the beach.
We got a "behind the scenes tour" at the Halekulani, for their refurbishments, but I do not recall any details on HWAK. I would contact the Halekulani directly, and ask specific questions.
I love the venue, and for pu`pus and a drink, it is great. However, for actual food, I lean strongly to La Mer, or Orchids. Also, each of those has a much better wine list, if that is your thing.