So here's the thing about forest service special use permits:
Every single one of them has an an annual review, and one of the things in the annual review is the question "does your company provide every reasonable accommodation to the public?" If the company does not reasonably accommodate, they stand a chance to lose the permit.
I know this very well because the company I manage has a forest service special use permit, and the year before I was hired, the company was on probation with the forest service for failing to serve the public, and catering to special interest groups solely.
In this context, with literally every single other ski resort on public land allowing snowboarding, I do not see how alta has any legs to stand on.