Actually, Night Slash gives Justified Pokemon like Cobalion a free boost, and that's not something we want, either. But then again, Shadow Claw vs. Night Slash is such a small matter there's no point arguing about this. It's a bit like arguing about Recover vs. Roost. Just have one up on the set, the other in Other Options.
The only perk of using Night Slash in UU is that frail Normal-types can't set up on you as well... But the only Normal-type with set-up moves that comes to my mind is Porygon-Z.
But as opposed to OU, where Virizion AND Terrakion roam, and Normal-types are virtually non-existent, UU has a few viable Normal-types. So Shadow Claw is perfectly acceptable. Also, Cobalion is gonna set up on you regardless of if you're locked into Shadow Claw or Night Slash. You have to switch no matter what (unless, of course, you're Life Orb'd).
-Zane
P.S. In regards to the "support" set, I just don't see much of a perk to using it. Aerodactyl is much more threatening (and also boasting an arguably better immunity to Ground-type attacks, rather than Electric-type attacks), even without a Choice Band or Life Orb, where as Dugtrio can barely scratch anything without an item boost... And being good at launching a Stealth Rock is pretty much true of any fast Pokémon with a Focus Sash. I don't know. It just doesn't make sense anyways, with Team Preview, that anybody would send out anything weak to Dugtrio as a lead. Most players are smart enough to hold on to their Victini 'til Dugtrio's felled. Also, I think TechniTop can COMPLETELY ruin the set... and Hitmontop is very common.