I suppose if Kornel really cared about giving his nondescript Hell Demons some character, he could make the Knight's and Baron's aversion canon and just program in a 'cost' pathing algorithm for them.
By 'cost pathing' I mean that, say that in order to path to any specific place, the AI would find the least costly path. Normal floor/water would have a cost of one, and say acid has a cost of 5. In order to convince a hell knight to path into acid, then the acid path would need to be a shortcut that would avoid more than 5 normal tiles.
Just an idea.