This is certainly true. It may sound strange to us now, but after August 1945, Japanese had been flung across East, South, and Southeast Asia. There was little ability to bring them home in orderly fashion. Tens if not hundreds of thousands of Japanese in Manchuria simply never return. Many were used as labor by the USSR and died in camps.

I can only speak to the situation in Vietnam, but beginning in 1945 (after Japan ousted the French colonials in a March 1945 coup), the Japanese gave military training to certain Vietnamese religious groups like the Cao Dai and Hoa Hao. When the war ended in August 1945, a significant number of Japanese belatedly followed through on their 'Asia for the Asians' slogan and joined the Viet Minh revolution as advisors, officers, and technicians and played important roles from 1945-1949. The DRV/Viet Minh nationalized them as người Việt mới (new Vietnamese). After non-communist groups split with the DRV and began fighting against their old allies, the Japanese advisors stay on as advisors, machinists, or radio operators.

But in fact, Japanese were on both sides initially. The British occupation forces under Douglas Gracey in southern Vietnam temporarily re-mobilized thousands Japanese soldiers and sent them against the Viet Minh in late 1945. They were reputed to be more violent and more successful. The Viet Minh reached similar conclusions. Referencing the role of Japanese deserters fighting against the Dutch in the East Indies, certain leaders argued that the Japanese troops produced deep fear in the returning French troops. A Japanese officer, Toshio Komaya, organized the DRV military operations in northern Vietnam in 1949 that opened the Sino-Vietnamese border and brought Chinese communist troops & advisors over the border to aid the DRV.

Christopher Goscha, "Building Force: Asian Origins of Twentieth Century Military Science in Vietnam," Journal of Southeast Asian Studies 34, 3 (2003).