^The Knights of Ren are not the Sith nor are they bound by a set credo or dogma other than the veneration of the dark side and are generally more flexible in terms of their outlook. Hence why in Crimson Reign, they allied with the Crimson Dawn against the Empire and assisted the Sith Eternal cult and the First Order when it was in their interest to do so.
Should their leader judge the actions of either faction to be damaging to their own interests or ambitions then naturally they would I don't see how this would be a contradiction.