Under your understanding of the language, every party to ever wage war with the US, from Mexico to Japan, has somehow committed "treason". Clearly, one has to be a US citizen and subject to US constitution jurisdiction to be able to commit treason, and the member states of the CSA had formalized their secession from the union prior the event that I am sure will insist began the war. So, unless "attempting secession" is also mentioned, you've got nothing.
No, to commit treason, you must be a United States citizen.
Mitsui Fuchida did not commit treason, Tokyo Rose did.
Where has it been determined, in U.S. Law, that the secession of the Confederate States was legal. If that has not been legally established, those men that served the Confederate Army and State remained citizens of the United States and could have been charged with treason.