From 2:00-8:00, even though I understand why they did it. Why wasn't stating their allegiance to a foreign government considered treason like it would be today under similar circumstances?

Same reason that the guys who went to the UK to fly for the RAF.....we just kinda looked the other way and they were technically " for hire" mercenaries. We have em today all over the world working for all manner of governments and groups.
The men who flew for the RAF were probably the closets to violating the law but , wisely, the feds simply looked the other way.

They were contractors. Treason would have only come into play if China was fighting the US or if they were still US military at the time of their Chinese contracts.

In a related note, I used to work with a guy who many years ago worked for a certain US government agency in Latin America in the 1980s. He told me that when foreign governments catch a mercenary (this isn't universal, just some instances), they are really CIA, or some other government's agency employees or contractors.

This is a really good question and kind of goes in line with my thesis. Even though it's 1812 vs. 1940, it's a question Americans have dealt with for our entire history. Don't forget the Americans who fought in the Spanish Civil War in the 1930s.

There may be, but if not, there should be, a book tracing American views on this throughout time. In 1794, we passed the Neutrality Act, to prevent privateers from serving for England or France during the Napoleonic Wars, but this was flouted often. Other nations had similar laws. Just finished a book on Confederate Raiders and England had a "Foreign Enlistment Act" meant to deter this kind of thing, but their leaders often looked the other way. A lot of times, these laws are only on the books to provide the veneer of government disapproval for the sake of plausible deniability.

Part of their deal was that if America entered the war they could return to their prior service without loss of grade. Several accepted induction into the US Army in July 1943 and were part of the 23rd Fighter Grp.

The pilots of the AVGs worked for an American company called Central Aircraft Manufacturing Company (CAMCO) which was created by William Pawley; a Curtis-Wright sales representative in China. They were hired as instructors and metal workers. ( Daniel Ford. Flying Tigers: Claire Chennault and His American Volunteers, 1941-1942)

I will say that Greg "Pappy" Boyington, in his classic memoirs, has little good to say about Chenault, and I imagine Chenault has little good to say about Pappy. Although I loved the show Black Sheep Squadron, the real Pappy was insubordinate to a fault, and I tend to agree with Chenault.

Years ago (98-99) there was a restaurant in Columbus, GA outside of Ft Benning that had some really cool Flying Tigers memorabilia. It was pretty humbling looking at the stuff in there.

It was owned and run by an Asian lady that I always believed was Chenault's widow, but from reading this article it may be Losonsky's widow. Also looks like they were pretty well paid.

http://www.azfamily.com/story/19907013/2012/10/24/military-matters-flying-tigers