Well, Tommy-boy has manged to quash any hope of the Blood Elves allying with him, I reckon he'd be even more upset if he knew just who they'd hidden and succored after that attack in 1990. That Hogwarts saw fit to bring those three to the seat of her mind indicates that she knows something they don't; I wonder if the "lost" Slytherin line is in one of their ancestries.
He may have screwed that up royally but it will still add burden on Potter. So it's still has positives for the Dark Lord. Oh yeah, she's got things up her sleeve.