Lum Berry is run on SD Sandslash for precisely this reason, Missy would just end up eating a +2 Night Slash or Stone Edge and dieing. Sableye, granted, would pose a problem.
Can we just agree that both Sandslash and Claydol suck and are terrible ?
Claydol outclasses the hell out of Sandslash in RU. What makes you think it'd be any different in UU?
Claydol might not be the best Pokemon to use in UU, but it's really the only choice for replacing Donphan.