In order to answer your question, the first thing needed is to understand clearly what the Aruch HaShulchan is actually saying in the citation you bring. He is discussing there the subject of the requirements of blessings and specifically over what things we study is it required to make the blessings for Torah study.
צריך לברך בין למקרא, בין למשנה, בין לגמרא, בין למדרש, והיינו מדרש המקראות במכילתא וספרא וספרי (רש"י ברכות יא ב). ודע שיש להסתפק בלומד דברי אגדה, כמדרש רבה או חכמת הקבלה
"It is necessary to bless whether for the written Torah, or for the Mishnah, or for the Gamarrah, or for the Midrash, meaning the Midrash on the written Torah in the Mechilta, and Sifra and Sifri (Rashi on Brachot 11a). And know that there is a doubt in regard to study of the words of Agaddah, like Midrash Rabbah and the wisdom of the kabbalah..."
What the Aruch HaShulchan calls 'Midrash' he limits only to the three halachic midrashim found to the last three of the five books of Moshe like Rashi explains in tractate Brachot 11a. All other midrashim he calls 'Aggadot' which is from the same root as 'Haggadah' and 'Naggid' which mean 'to tell'. It means the oral tradition that originally was not permitted to be written down, but only shared face to face from teacher to student like is found in Gittin 60b and Temurah 14a.That portion of the oral Torah comprising Mishnah and Gamarrah also fell under this same restriction originally.
It was only as external troubles (like poverty and servitude to foreign conquerers) increased for B'nai Yisrael, and the level and quality of learning decreased, that compromises started to made in some areas. This was done so that the oral teachings, particularly those relating to proper practice of the commandments materially and physically, would not be lost like is recorded in the Igeret of Sherirah Gaon 1:1. Some parts of the oral teachings began to be written down. This is based upon the principle from Mishah Avot 1:17 taught by Rabbi Shimon be Gamliel that "the deed is the primary thing".
The more esoteric parts of the Torah remained oral and in some cases had a restricted circulation to only select, gifted and talented individuals. Over time and as the suffering increased, this writing down of the oral parts grew and expanded to include other areas of the oral teachings. Again, the more esoteric portions, even after being written down, were often restricted to small circles of select individual. And this continues even to this day.
But many of the esoteric materials, particularly following the time of the Ari z"l, Rabbi Yitzchok Luria, have been allowed to be circulated in increasingly broader circles until today, many books from ancient tradition and teaching are readily available.
What the Aruch HaShulchan is referring to as the 'wisdom of the kabbalah' is talking about these highly esoteric, but authentic teachings, which have been passed down from generation to generation since Moshe Rabbeinu and even before.
They comprise the same teachings in 'kabbalah' that we have always had. Examples can be found in Sefer Yetzirah, Sefer Pirkei Heichalot attributed to Rabbi Yishmael Kohen Gadol, Sefer HaTagin attributed to Yehoshuah be Nun, Sefer Ma'ayan HaChochmah attributed to Moshe Rabbeinu, Masechet Atzilut from the time of David HaMelech, Sefer HaBahir, Sefer HaTemunah and Sefer HaKaneh attributed to Rabbi Nehuniah ben HaKaneh, and even Sefer Raziel HaMalach attributed to Adam HaRishon, Sefer Chanoch attributed to Chanoch ben Yered from Sefer Bereshit, and Sefer Noach attributed to Noach ben Lemech of the story of the flood and Ark. There are many other examples.
It should be noted with all this that even today, there are some manuscripts which still are not published and have extremely limited circulation amongst the Jewish people.
For someone who actually looks at these sources, it can be seen that kabbalah, what the Aruch HaShulchan refers to as "the wisdom of the kabbalah", is the same kabbalah that has been passed down through all the generations going back all the way to Moshe Rabbeinu and even before.