If something adds only luck to the game and no strategy, is there a reason to allow it?
Most moves have some intrinsic luck element, but they also have far more significant strategic implications. Moves such as Attract and Confuse Ray may be mostly luck-based, but they, too, have significant strategic implications, as they can be cured by switching, unlike evasion boosts to your opponent. Also, Attract only works on certain Pokemon, so assuming you don't foolishly set all of your Pokemon to the same gender, it should be a simple matter to bring in one that's immune to the move.
Sand Veil's problem is that it's an intrinsic part of certain Pokemon. Not using Sand Veil means not using Garchomp, and not using Sand Veil + Sand Stream means not using Garchomp on the same team as Hippowdon or Tyranitar. Both of those have strategic implications on their own, rather than being purely luck-centric. Even if those Pokemon get their alternative DW abilities, banning the combination might have other strategic limitations, since it would have other movepool limitations. So... I don't know what to do with regard to that.