I recall reading that somewhere, but Zumwalt could only recommend the award. The decision would be made higher up the chain of command. I seriously doubt that a Navy Cross would have ever been awarded for the action described.
Thanks for the comments on the award authority chain. I find this whole aspect of Kerry's record quite puzzling, with respect to both the award itself and Johnson's quotation of Zumwalt on the alleged Navy Cross consideration. If Zumwalt had personally reviewed the paperwork on the incident with a close eye (and he may not have--he was after all a busy man with many more pressing responsibilities--which might help explain things) I don't see how he could have considered a Navy Cross--even putting the best face on Kerry's reported actions as his supporters do, it's difficult to interpret his actions as meeting the criteria for that award. I suppose one possible explanation is that Zumwalt may not have reviewed the paperwork on the incident too closely and may have been using hyperbole during the speech where Johnson quoted him. At the time Zumwalt's son had either just died or was near-death from what Zumwalt attributed to Agent Orange, so the Admiral was going through some personal issues and was making attempts to heal some old wounds, which is what led him to reconcile with Kerry temporarily at that time (he later recanted). So that may have colored his comments, which is the best explanation I can come up with for the statement attributed to him by Johnson. I have pondered a few other possibilities but that is the one that makes most sense to me. In any case something does not add up here.