Well, it seems from Dark Serge's demonstrations that the Flame's power has to be consciously used. The Flame basically responds to thoughts and dreams, so I don't know how Serge can subconsciously use it to see things he doesn't want to see. (Like his own demise.) While it probably is the Flame, I just wanted to play with the possibility that the prophetic dreams is his innate magic or something. XP
Also, in the Unified Timelines, Serge still remembers the events of the game, when Schala, who should logically be aware of the Flame's abilities to give Serge visions (if it has such powers) distinctly said he wouldn't remember anything. And yet he does. And depending on how you interpret the Unified Timeline, he might not even be the Arbiter anymore when this happens.