I have previously mentioned how Arneson was supposed to have a cameo role in the film. His main role seems to have been a kind of technical advisor as well as being supposed to write a module based on the film:
"[We]evaluated the scenes in D&D-specific terms. After all, we are doing the module! Many D&D elements are not obvious in the movie, but they ARE there. Short of having a technical readout for each rule along the side of the screen, it was seldom possible to stop and explain what is going on, rulewise. After all, this is a movie, not a documentary." (-On the Set of the D&D Movie, by Dave Arneson)
In retrospect, it seems like this was a poor use of having a man like Arneson on the set. Perhaps instead of consulting him on rules, the director could have asked for creative input? Based on his descriptions from the set Arneson seems to really have enjoyed himself though, spending time with the actors and being given a chance to talk about D&D to both cast and crew.
As mentioned, Arneson was originally asked to make a module based on the movie. While this project was cancelled by WotC before the movie was released, private correspondance between Arneson and fan Robert Blezard suggests that Arneson loved the opportunity to be able to work with D&D again. It is not unlikely that this was one of the things that made him want to bring back Blackmoor again, which was released only a few years later (2004). So perhaps something good came out of the D&D movie afterall? Besides Thora Birch of course! :)