Listen up, "disreproachable" is absolutely a word. I am not saying you hear it every day; in fact there is a significant, not-insubstantial chance you won't even hear it in your lifetime. You should get out more.
It's very much like "irreproachable" and its root word "reproach" but in no way similar, other than the obvious similarities.
Obviously similar uses:
"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.