Just My Happence,
Rav hai Gaon is known to have learned Kabbala and even wrote some Kuntreisim on that, but when did you hear about Rav Saadya Gaon? His Pirush on Sefer Yetzira doesn’t seem to have anything to do with Kabbala. Although, there is a reference to an interesting tradition from Rav Saadya, about how to make a Golem, mentioned in the Kol Yehuda on the Kuzri. Also, the Yashar Micandia writes that the fact that Rav Saadya Gaon wrote a philosophy based Sefer doesn’t show that he didn’t know Kabbala as well. But where do we find his name in reference to Kabbala?
Actually, utilizing the idea of the Yashar Micandia it is in fact possible to say it is not a Stira. I mentioned earlier that his problem with reincarnation is that the Nefesh, being the identity of this particular person can’t be redifined to be the identity of another. But the Magid Meisharim actually explains that a new Nefesh is created for each new Gilgul. So, perhaps being that Gilgul was such a secret in those days (that the Ramban refused to mention it explicitly in his Pirush on Iyuv), he neglected to mention the true concept that is reminiscent of that other idea he was discussing, which is the popular Hindu concept of reincarnation.
R’ Crescas’ relation to Kabbala seems to be more similar to that of the Sefer Ikrim and the Abrabanel among many others. They respected it, and even looked into what was available, learned through the Sefer Hazohar, but did not consider themselves Kabbalists. The Abrabanel writes of himself, “Eini Mei’anshei Hachachma Hahi”, althoug he does discuss the Sfiros and different ideas from Sifrei Kabbala. In other words, he didn’t say, Oh I have no idea what this means. But, it wasn’t his expertise. The Chinuch mentions the existance of Kabbala, Mekubalim, and that they have much better reasons for the Mitzvos than his.