@Yoshistar888 The keeper said it was smooth, but his English was not good. Actually, on second thought it might just be a scalloped. Another picture I have of it had subtle notches on the cephalofoil. Guess I still have to go to Ibaraki for a real smooth hammerhead to add to the gallery.
I just sent a message to the aquarium. When I asked on Facebook, people said it's possible for a smooth hammerhead to have deeper notches on its cephalofoil that makes it look like a scalloped.