It’s “possible” to be DPS as any build with any class. Such a silly question. The issue (if you see it as one) is that you won’t be as good as frost or unholy. Blood is at its best when you have no one else to heal you. When you do have a healer, which is the case in any group/raid, its main perk is negated. What you are then left with is an inferior talent page. Both of the other pages can tank+damage better. They just don’t have the personal healing.
“People thought they were crap, but they aren’t, they just can’t pad their damage with AoE.”
-Pad their damage? Damage is damage. If one guy has a higher total, then that means he did more. It does not matter where it came from.