True. Although I'll guess the Soviet system was probably better than what some of those countries had before anyway. Actually I'll correct what I said when I included Yugoslavia, they were entirely independent from the USSR, and I'm not sure what they did regarding the status of athletes and profesionalism in sports. I know they did have Mate Parlov, light-heavy gold medallist in 1972 Olympics, and professional WBC champion at light-heavy in 1978.
Lots of German boxers competed internationally on the professional stage before the war. Lots of foreign opponents were brought to Germany to compete too. There doesn't seem to have been an issue, unless I'm missing something.