It is not a Hopper thing. They are also hidden on the ViP's. For a couple of months each year, from early November to early January, some of the AUD channels are un-hidden and made available in free preview for the holiday music. Usually, those channels get hidden again after the preview ends, but sometimes Dish (accidentally?) leaves those particular channels un-hidden and red in the guide the rest of the year, only to hide them again after the following year's free preview.
I think it is kind of the opposite. The AUD channels were always available in AT250 (since when the package was introduced as AT150) and Dish hides them from non-subscribers because they don't want customers with lower packages calling them to request those channels as a separate package. (The idea being that not many lower-package subscribers would upgrade to AT250 just to get those channels, but they might be willing to spend a few bucks per month to add just the AUD channels. Either Dish is contractually not allowed to sell them as a separate package, or they just don't want the hassle of offering such a package that they think very few people would be willing to pay for, especially with so many other music channels already included in lower packages.)