In 1957, Rav Waldenberg was asked whether one has to take ma'aser from reparations made or recovered from Germany as a result of their seeking to restore what the Nazis had forcibly taken from the Jews during the Holocaust. The questioner, Dr. Pinchas Wolf, assumed that no ma'aser needed to be taken, since the money or possessions that we being returned were actually the property of the recipient all along.
Rav Waldenberg argued that, in fact, the opposite would be true. Given the nature of the Nazi regime and the brutality with which they treated the Jews, with regard to their taking property from the Jews they would have the status of armed bandits. When a person has his money or other possessions taken from him by such individuals or gangs he is assumed to have יאוש, to have despaired of ever seeing that money again. Thus, if the money is ever returned to him it is considered to be not a return of the lost money, but rather a new infusion of funds that are thus subject to the laws of ma'aser.
Rav Waldenberg concludes by citing the Sefer HaChassidim, who discusses the important of giving ma'aser, and among the cases when one must give ma'aser he includes someone who finds a stolen object. Recovered funds or possessions that were taken by the Nazis certainly fall under the category of stolen objects that have been found (and whose owners have despaired of ever getting them back), and thus one should give ma'aser from these recovered funds.