I realize that to cleave to God is not as exclusive as having the right set of beliefs. But nor is it irrelevant to ones's beliefs.
The way I see it is that it is really in the realm of the Ding An Sich as Schopenhauer would put it. That is to say God is simply beyond pure Reason and reaching Him is possible but not by means of having a right set of beliefs. Cleaving to God is possible even with mistaken beliefs. And even with right beliefs one can be far from God.
The Rambam already in the Guide that people have no inherent sense of the Divine Law or Moral Law. We depend on the one time revelation on Mount Sinai. A Unique event in History.
That is there is no access by means of reason. But there is access by faith.

I feel there were great people that had basic belief in Torah and yet maybe had a few things off. Still i think there were connected with the Divine Realm. I do not think purity of belief is much of a proof or criterion for being kosher. The Sitra Achra has plenty of agents that can get through that  test.