The fact that Rav Nahman of Breslov had some statements about Torah scholars who are demons certainly was not just an abstract idea with no relevance to action. Rather he certainly meant this to be a starting point assumption until you know differently. That is, in order to be safe, you assume this as your starting point. And then if after careful investigation you discover differently, then OK.
But there are plenty of other important principles in the works of Rav Nahman.
The main ones are private conversation with God constantly, learning by saying the words as fast as possible and going on, and the well known Tikun HaKlali. [That is a correction of sexual sin by saying ten psalms 16,32,41,42,59,77,90,105,137,150]. But other good advice does not diminish from the value of even one piece of good information about the problem of Torah scholars that are demons which one ought to assume from the start until proven otherwise. I mean to say that his suggestion here is that one ought to assume all to be guilty until proven otherwise.
[It is constant in Rav Nahman's writings these points. However to my own satisfaction, I have seen the importance of the Gra, Rav Israel Salanter and Rav Shach. In fact, I would highly recommend that basic straight Torah path to others also. That is more or less what is called the "Litvak Yeshiva Path"]