For some reason, Dark type pokemon has kind of shitty distribution for moves and abilities.
Hydreigon and Tyranitar are fucking great, we all know that.
Zoroark, Umbreon, Sablye, Honchkrow and Bisharp are all viable. Bisharp has the hardest time in OU out of those, just because the top shit in OU all resists Dark anyway.. But the others have their place, and all do great in UU.
Scrafty was OU for a pretty long time, and can definitely play there. Reason it got booted was stats.. it became the lesser choice when compared to shit like Terrakion. It still works just like it did before, though.