Are there any responses by Rishonim or Aharonim (even contemporaries) against those who criticize the Kabbala and the Zohar done by many people? Like this accusation. Some people claim the Zohar doesn't fit into the Torah. They claim it contradicts the Torah. They claim the Eser Sefirot are against the Torah because it Has WeHalila "split Kudsha Berich Hu into ten." Are there any Gedolim who discuss this topic?
Look in Derech Mitzvosecha [Mitzvas Ha'amanas Elokus (Mitvah of Belief in G-d) Chapter 3 and onwards] where the Tzemach Tzedek of Lubavitch discusses the question concerning unity of Hashem and the Sfiros.
You might want to check out "Iggeret Chamudot", by R' Eliyahu Chaim Genazzano, an Italian Kabbalist of the 15th century. Part of the main focus of this work (actually a letter, I think) is to rant against those who employ "speculative reasoning" and philosophy in their quest for religious truth instead of kabbalstic tradition. The sefirot come up, of course, as well as other kabbalistic concepts, but I don't think it is much of a detailed defense of kabbalisitc ideas found in the Zohar.
If you're looking for explanations of how the sefirot don't contradict God's "indivisibility", I have come across explanations for this in the works of Rishonim, but I can't point to exact sources at the moment. The general idea is that the sefirot express God's attributes, not His essence. The same way we would be able to say "God is kind" without necessarily saying that "kindness" is "part of" God's essence as a separable part of His being.
Also what comes to my mind is Abarbanel's lengthy defense of the Zohar's concept of reincarnation (which, incidentally, is one of the ideas that the linked video calls antithetical to Judaism) from those followers of Aristotle who denied its veracity.
See http://onthemainline.blogspot.com/2011/12/marc-shapiro-on-question-of-obligation.html ans all the links therein.