It's very much like "irreproachable" and its root word "reproach" but in no way similar, other than the obvious similarities.
"Her grooming was beyond reproach; it was _irreproachable_."
"His groomering was _dispreproachable_; although without question I burned the couch cushion he sat on when he left."
"You know how 'irreproachable' is a word? That's awesome, but I don't think 'disreproachable' is cool like that. Only a choad would say that."
"You know what word I like? 'Disreproachable.' That's an awesome word. I don't think a chode would use that word."
So, they are not completely interchangeable, but you definitely get the picture. Also, New Moon sucked. Where I come from the vampires actually suck blood. Come on.