Wait, with a double blind character selection, you also have to pick your ultra blindly?
"When a player request Double Blind, the player on the left side (1p) decides which characters and modes (e.g. ISM, Assist mode, or Ultras) they will choose and whispers his selection to the Judge.
The Judge then signals the player on the right (2p) to pick his characters and play modes.
Once the player on the right (2p) has finished, the Judge makes sure the player on the left (1p) sticks to his original choices."
If you know your opponent's main, you could request a blind pick and hope they choose the wrong Ultra.