HAL is not involved directly, but they're credited because of the original game code. They offered Melee to Sakurai to use as the base for Brawl, and since this game looks to be built off of Brawl, HAL's original code remains in some form. I think Sakurai said the only HAL employee who worked on Brawl was a sound guy, and it's probably not much different this time around.
Some of the people who worked on Uprising are on the new team. The development structure is pretty similar to Brawl, actually -- there's a big studio at the core with hand-picked staffers filling out the rest of the team, only instead of Game Arts it's Namco Bandai.