When approached, a company representative simply confirmed to Joystiq "there will be no DLC for the Wii U version." We'd asked for an explanation, and to confirm the DLC would definitely not arrive on the platform at a later point, but he offered no other comment.
It's a curious turnaround by Ubisoft, having released DLC for the Wii U version of Assassin's Creed 3, albeit typically a while after it had arrived on other platforms.
Assassin's Creed 4 itself safely docks on Wii U, as well as PS3 and Xbox 360, on October 29. It then sets sail for PC on November 19, and the Xbox One and PS4 at their launches.