I'm probably missing something, but it doesn't seem to me to be a legal threat if one editor notifies another editor that the latter's participation may raise UCMJ or regulations problems. This is not the same thing as threatening to sue. Nor does it strike me as a legal threat to note that some members of the armed forces may be compelled by UCMJ or related regulation to report on-wiki activity that looks like a serviceman (or servicewoman) violating regulation or policy.
To me, a legal threat would look something like this: "If you don't do X (or cease doing Y), then I'm going to report you to the authorities and get you in trouble with your CO." It would *not* look like this: "I'm just letting you know that your participation in this way may create problems for you under the UCMJ or regulations, especially because some of us are obligated by that legal framework to report apparent violations."
--Mike