At least, not how I interpret the definition of cheating.
To me, cheating would be to hook his mortals up with certain quest skills or benefits, either directly with his Imm, or indirectly by asking other Imms to do it for him. Nepenthe didn't do that.
Rather, Nepenthe had immense knowledge at his fingertips, and knew everything there was to know about skills, equipment, areas, quests, etc., and it was impossible for him to play the game without using some subset of that knowledge. In my opinion, that is not cheating.
In fact, Nepenthe held himself back a lot of the time, generally avoiding pushing the pendulum too far in favor of one cabal by either deleting early-ish, or flying under the radar. For example, I was the Fortress leader at the time of that paladin you mentioned, and while he was obviously competent, he never really changed things that much or involved himself in the direction of the cabal. He also deleted early on, while the Fort was in the midst of a constant upswing. Most of Nepenthe's characters were like this.