Is the book Sefer HaRazim heretical?
Does it play any part in kabbalah? If so, is it still used by kabbalists today?
Rabbi Avigdor Shiloh wrote in this Q&A that in general, there aren't discrepancies between the Talmud and Sefer Harazim, although some of the things outlined there are no longer applicable per halacha.
Mordechai Margulies, in his edition of the book, wrote that historically, the book is known to have been used by rabbis in the time of the Gaonim, because some of the Karaites (such as Daniel Al-Kumisi and Yaakov Al-Kirkisani) criticized these rabbis for using books such as this one (pg. XII). Furthermore, Rabbi Elazar of Worms quoted the book extensively in his book Sodei Razaya, although he only quoted the more theoretical parts and not the acts and oaths and the names of angels (those found solely in Harazim) (pg. XIV). Books that may have been based off of Sefer Harazim include: Charba D'Moshe, Sefer Adam, Sefer Hamalbush, Sodei Razaya, Sefer Raziel.
I don't personally know any kabbalists (at least, not that I'm aware of), but I'd guess that like the Roke'ach (Rabbi Elazar of Worms), if the book is still in use today, it's the theoretical portions that are used.