"Heil Roosevelt" was not a common phrase in American culture. The only documented instances of this phrase being used is by Americans in Germany retorting to the greeting of "Heil Hitler." This included famously the U.S. Olympic Rowing team during the 1936 Olympics in Berlin. Margetta is more likely making a reference to Franklin D. Roosevelt and Adolf Hitler being in power for the exact same duration of time, 1933-1945.

Source: The Boys in the Boat by Daniel James Brown