Well, that question might clarify the issue for Etzioni, but I'm at a loss to see how. In the original scenario, the journalist's duty to "objectivity" or "the story" is placed in conflict with the journalist's duty to country. In Etzioni's version, the two duties are in harmony, both arguing in favor of not warning opposing troops. What light, then, does it shed on the more difficult original case?
A more revealing hypothetical would place the journalist among a criminal or terrorist gang about to ambush and murder a group of police officers, or innocent civilians--or even members of the journalist's own family. Two points are thus illuminated:
The question is thus not, "what should a loyal, law-abiding American journalist do when traveling with soldiers ambushing Americans, or criminals or terrorists ambushing their victims?", but rather, "what is a loyal, law-abiding American journalist doing consorting with troops fighting against Americans, or criminals, or terrorists, lending them legitimacy by trusting in them so completely?" If the answer is, "there's nothing wrong with that", then obviously there's nothing wrong with the journalist cooperating with his or her hosts in other ways as well--such as keeping mum about one of their impending atacks.
At that point, the journalist has effectively become an accomplice, and American troops or police should be expected to deal with him or her accordingly.