User blog comment:Roranoa zoro/D.F. USERS SWIMMING!!/@comment-1595565-20101220025521

Impossible. Haki and water only cancel out the abilities bestowed by the devil fruits and saps their energy, or it saps the persons ability to use it, like when Sanji was still able to pull Luffy's head to the surface even though he was unconscious and pinned down by a rock. It is unknown currently if haki is affected by water. However, as far as anyone can tell, the ability to swim is not regained when under the effects of haki. Haki simply appears to allow the user to hit a devil fruit user, not cancel anything.