Just like in real world medicine, I believe that Tsunade and Kabuto, while both being medic-ninja, specialize in different fields.
From what we have seen of Tsunade, she specializes in using her chakra to "heal." She healed Sasuke and Kakashi's mental incapacitation via Tsukuyomi, she healed shinobi in the second world war that were poisoned, she healed the kage and shinobi alliance with her chakra, and her disciples are both able to do the same things.
On the other hand, Kabuto always stood out to me as a surgeon. That is to say, he specializes more in the cutting open of bodies and doing things with them. He cut open the anbu bodies in the earlier parts of the manga (when he replaced one's face with his own and animated it's body to allow him to escape Sasuke's hospital room,) all of the cadavers he carries in his scrolls to fool enemies, and finally the surgery that he did on himself to allow him to utilize all of the powers in the end. The injection of his navel snake directly into Sasuke's body (be mature) also lends itself to direct body alterations.
This is not to say that Tsunade has not done surgery (she in fact did a surgery to return Lee to his ninja career) or that Kabuto does not use his chakra to heal (he healed both Hinata and Sakura from a distance at different points in the manga) but rather that they tend to lean more towards those specialties. What do you think?