[Frostmourne27]

You might want to consider what JaydedOne said, but sending them a letter might not be a bad idea. Or reading around on their web page. I know nothing about DnD miniatures, but you might make a case that your use is open game lisance (spelling?) if your mod resembles greyhawk type worlds. One the other hand, this is hardly widespread, so they probably wont care, and as BigJMoney pointed out, worst case they probably will do nothing more than send a few insulting letters demanding you stop publishing your mod.