In reality I wouldn't, since I am not a theif.
You're never ethically obligated to be unethical.
The question is are you ETHICALLY OBLIGATED...
You cannot be ethically obligated to be unethical.
Many argue that ethical rules can be relaxed under certain circumstances, but Insom does not present such a scenario and it is not up to the answerer to add one into the question.
But even then, it's going to take an even larger argument to make it an ethical obligation.
And Insom makes it clear that stealing the wallet will have no effect on the future.
Even if you knew Hitler was going to do what he did and blah blah blah, it is still unethical to steal his wallet.
Therefore, you cannot be ethically obligated to steal it.
The only sound answer to this question, as it was stated, is "no".
Didn't you folks take any philosophy courses in school?
Also, I wouldn't. I would gain little, and given the levels of inflation in 1930's Germany, it would be worthless after a day.