The Smash Ultimate website has updated with a list of all of the composers that worked in the game and some of their previous work - including Nintendo composers:
Soshi Abe - The Legend of Zelda: Breath of the Wild DLC
Yasuaki Iwata - The Legend of Zelda: Breath of the Wild / Mario Kart 8
Koji Kondo - Super Mario Bros. series / The Legend of Zelda series
Naoto Kubo - Super Mario Odyssey / Captain Toad: Treasure Tracker
Maasa Miyoshi - 1-2-Switch / Miitomo
Ryo Nagamatsu - Nintendo Land / The Legend of Zelda: A Link Between Worlds
Yumi Takahashi - Nintendo LABO / Miitopia
Kazumi Totaka - Animal Crossing series / Yoshi series
Shinji Ushiroda - Rhythm Heaven series / Donkey Kong series