Hitfix has confirmed that Jason Momoa will play Aquaman in Batman v. Superman: Dawn of Justice. They're also reporting that Zack Snyder's already finished the character design so that filming can begin as soon as possible
The rumor that Momoa would be in the project has been floating around for almost six months, with Aquaman listed as one of the options even back then. But Momoa denied it as recently as a month ago.
Hitfix also confirms earlier reports that Aquaman's appearance would be as someone not at all happy with the outcome of Man of Steel, since the World Engine screwed up the Indian Ocean. The character's not a main character — like this film has room for that — but he is being introduced in order for him to return in the Justice League movie. No word yet on whether he'll be going by the actual name "Aquaman" or by something else. [Hitfix]