Actually, the senior scientific positions Manhattan Project were largely (some 50%) filled by Jews, many of whom were ejected from Nazi occupied Europe. Shows how goddamned smart those "pure Aryans" were.
The reason who so many Jews were willing to work on the project was that they feared that the Nazis would get it first. Remember, Otto Hahn who first discovered nuclear fission was a German. Heisenberg was also a German. Both worked for the Nazis on their poorly run uranium project.
Hahn and Heisenberg knew that a bomb was possible in principle, but did not know how to do it in detail. They were afraid to tell the high ranking Nazis (including Hitler) because if they were given resources and FAILED, they knew what would happen to them. Another triumph for totalitarianism.