Zumwalt's tumblehome hull in heavy seas

Does the Zumwalt class's tumblehome hull make the ships poor in heavy seas?

No; the tumblehome form is described as giving the ships smooth behavior in very heavy water.

The low, inward-sloping sides can make a Zumwalt-class destroyer look as if it would float poorly. That visual impression is reversed by the tumblehome hull's reported smooth behavior in heavy water. Seakeeping therefore has to be judged separately from the familiarity of a conventional flared hull. Photographs alone provide a poor basis for assessing the class in heavy seas.