"Won't even be noticed" is a bit of an overstatement, but I think the basic point is sound. The patronage of people who are actively engaged with the actual D&D game enough to be invested in the controversy is not necessary to power this movie to success or to keep it from failing. It's a major motion picture with wider appeal than active D&D players, but also generally subject to the manifold market forces that cause many big movies to succeed or fail.
Of course, to throw some cold water on that philosophy, while I think the OGL-engraged are unlikely to be a determinate factor in the movie's overall success, it certainly seems plausible that WotC executives having gone through what I'm sure is a stressful time for themselves (which they doubtlessly consider completely unfair and in no way their own damned fault) will be so hyper-attuned to any hint of OGL-gate impact on their bottom-line that they will carefully look for any hint of fan backlash in the movie's numbers. But that seems to be imputing more competence and sense on the WotC executives than they've shown of late.
In any case the products principally marketed to actual D&D players are where the voices of the angry can most meaningfully be heard. The people upset about OGL-gate heavily overlap with the "whales" of D&D book-buying.
