I don't actually have access to Disagaea 2 novels, so no. But I really doubt that the author is going to paint it in a different light when Adell's reason has been given in-game, since he hasn't done anything to completely contradict canon as far as I know. (aside from Disgaea 2 taking place 120 years later)

What in-game chapter is this revealed in? Sometimes the Japanese drop comments about the novel on play vids, so if the author did give him a different reason, they'd probably mention it.