С японцами было не так просто.
Например:
http://www.modelminority.com/article900.html
"During World War II, a substantial number of Asian-Americans served in America's armed forces. Approximately 25,000 Japanese-Americans proved their courage on the battlefield."
"The 442nd Regimental Combat Team, composed primarily of Asian-Americans, was the most decorated unit of its size with seven Presidential Distinguished Citations and 18,000 individual decorations, including the Medal of Honor, 47 Distinguished Service Crosses, 350 Sliver Stars, 810 Bronze Stars and more than 3,600 Purple Hearts."
100th Battalion, 442nd Infantry
The 100th Battalion, 442nd Infantry, is the only remaining Infantry unit in the Army Reserve force structure. Its headquarters is located at Fort Shafter, Hawaii, and its units are located in Hawaii, American Samoa, Guam and Saipan. Under the command and control of the 9th Regional Support Command, the 100th/442nd's wartime mission is to be one of the maneuver battalion's of the 29th Separate Infantry Brigade, Hawaii Army National Guard.
It is important to recognize the contributions of the Japanese Americans who served in the U.S.
// Дальше — www.globalsecurity.org
"These Japanese American units suffered an unprecedented casualty rate of 314 percent and received over 18,000 individual decorations. .. For its service in eight major campaigns in Italy and France, the 100th Battalion and 442nd Regimental Combat Team earned eight Presidential Unit Citations."
То есть на войну с Японией их не пускали, но воевать они воевали. И воевали весьма хорошо.
А с немцами в США было ЕМНИП намного лучше как во время Первой так и Второй Мировой. Ссылок не нашёл, но было их в войсках дофига, в том числе и на командных постах.
Моё ИМХО что безусловно как в США так и в остальных странах куда иммигрировали бывшие жители СССР, если будет война с Россией то они (вернее их дети, по возрасту большинство самих эмигрантов уже служить не будут в любом случае) пойдут воевать и пойдут куда пошлют. Ну может за редким-редким исключением.