Whether streaming or let's-playing a game is transformative enough to qualify as fair use is not specified by the statute in the U.S. anyway, is it laid out clearly anywhere? That means it's up to the courts, who decide particular cases, to render justice within the bounds of the law. So far as I know (that's not far at all), no court has decided this. I think it'd be premature anyway.
Nintendo are very strongly in the "videos of our gameplay fall within our copyright" i.e. are-not-fair-use camp (while they've been loosening their terms, it's only the not-fair-use view that gives them the right to dictate terms at all). Many others really don't care whether it falls under fair use because they'd give permission for streaming and lets-plays anyway.
Speaking purely for myself, it does not seem right or just to use a mod you were offered for free and asked not to make money on, to go ahead and make money on it anyway. "Inconsiderate" is too weak a word.