There is a wide range of credible, and not so credible sources in the field of Kabbalah.
I was wondering if the works of the Baal HaSulam (Rabbi Yehuda Ashlag) such as "Talmud Eser Sefirot" are considered kosher in orthodox communities?
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Rav Ashlag was considered by his contemporaries as a scholar of note as well as a mystic. He served as the Rabbi of Givat Shaul, Jerusalem in 1924. However, his ideas on Kabbalah were considered very un-orthodox and thus he was always considered a man of stature but also a fringe personality. Famously, he was an ardent socialist to the extent that in a meeting with Ben-Gurion the first Prime Minister of the State of Israel complained: “I wanted to talk about kabbalah, but the rabbi wanted to talk about socialism.”
As is widely known his philosophy has been used to disseminate "Kabbalah" to the masses Jew and non Jew alike, and has been grossly misinterpreted in doing so. This has turned off many people from his writings and philosophy (assuming people even know of the origins of the Kabbala Centre)
In summation, Rav Ashlag was a well respected albeit fringe personality in his day, the progenitor of a peripheral Kabbalistic philosophy and an avowed socialist. His legacy is complicated in the orthodox world, and thus I would not say he wasn't "Kosher" for he was greatly respected by the Rabbinic establishment of his time, but also I wouldnt say he was fully embraced in the mainstream of the Jewish world, and his works are approached with a small amount of trepidation mostly due to his self described students and legacy bearers have misused his teachings in grotesque ways.
See more here: http://en.m.wikipedia.org/wiki/Yehuda_Ashlag
I have seen Rav Ashlag's commentary on the Zohar (The Sulam) in many varying shuls and yeshivot in Israel and I have never heard of anyone who thought to exclude his works from the Orthodox canon. Many yeshivot do not promote the study of kabbalah so perhaps they would not have a zohar at all.
On the other hand, Philip Berg the founder of the Kabbalah Centre, was a disciple of Rabbi Yehudah Brandwein, the primary disciple of Rav Ashlag. He has NOT been accepted by the Orthodox community. The Kabbalah Centre also published an edition of the Sulam which they gave away for free and therefore it made its way into unsuspecting Jewish institutions. As far as I know the edition is the same as the standard edition. You can see a picture of it at this link Kabbalah Centre Hebrew store
Is the Mishkan Kosher? Though he was student of his times and environment politically, Rav Ashlag's connection with the Upper Worlds was so complete, and dominant in his days, that it would be impossible to say that the word "Kabbalah" would be on the lips of the world today, if it were not for this great sage. No man of his generation provided such an uncorrupted example of cleaving to the Creator, and the removal of ego. His indelible mark on the development and dissemination of this sacred wisdom will continue to grow in relevance, throughout the fabric of space and time, until the Final Redemption has been achieved by All of Humanity! His greatest wish would be for knowledgeable Torah Scholars to step forward and fulfill their sacred obligations rather than continue to obfuscate the true purpose of their studies and place in this world. We exist not for the sake of merely ourselves, but for sake of others in this world. When this is understood and practiced in our communities as a given, the great peace will arrive and our spiritual exile will end. Rodef Shalom.