Although not at Lady Tsunade’s level, Kabuto was an expert medical ninja. Before finding herself with Orochimaru, she was trained in medical ninjutsu by her adoptive mother, an elite spy for Konohagakure known as the Wandering Priestess, and a former member of the Danzo-led Foundation. In his youth, he spent his time helping heal the injured Leaf shinobi, his abilities first caught the attention of then-leaf Jonin Orochimaru.
Contrary to popular belief, Orochimaru’s relationship with Kabuto was definitely not that of master and servant. Kabuto agreed to help Orochimaru create a nation-less village where individuality is encouraged and celebrated. This was the birth of the Hidden Sound Village. True to his word, Orochimaru never sought unquestioned support from Kabuto. It was Kabuto’s medical ninjutsu skills that made him endear him to Orochimaru, but during their time together, Orochimaru came to value his judgment and advice. He never had to suppress his true personality. Kabuto was free to act as he saw fit, except where direct orders were given to him.
As for why Kabuto chose to heal Hinata, it must be just because he wanted to. Shortly before noticing Hinata’s discomfort, Kabuto stated to himself that Naruto’s match was the entertainment he needed before completing the monumental quest that crushed Leaf Village. It is second nature for medical ninjas, especially those who have been practicing since then, to heal the sick. It was not out of character for her to help Hinata, as she had nothing urgent to do at the moment.
Many theories suggest that Kabuto may have had a more sinister motive to aid the Hyuga heir, such as accessing his DNA to understand and possibly reproduce Byakugan. While this makes sense given both his and his master’s desire to acquire all the knowledge in the world, this does not seem right as nothing came of the event. throughout the original naruto serial and cargo, neither Kabuto nor Orochimaru implied envy for Byakugan or showed any techniques that could be derived from it. In fact, Kabuto may not even know that there is a Hyuga he has just helped.
Additionally, this wasn’t the only instance where Kabuto chose to help his “enemies” for no real reason. When one of Naruto’s tails crashed into Sakura during the Battle of Tenchi Bridge, Sakura eased his discomfort and explained that it would be advantageous for both him and Orochimaru for Team 7 to continue hunting Akatsuki. It would seem that Kabuto was perfectly happy to assist in any way he could with medical ninjutsu, as long as the person was not actively opposing either his or Orochimaru’s goals.