The simple fact of the matter is that physics was advancing at a steady pace. To stop nuclear weapons with a PoD after 1900 would require a major collapse of society. A disaster on the scale of the Black Death.
Even if Einstein isn't around, Special Relativity (which is where E=mc^2 comes from), is a direct result of the Michelson-Morley experiment. Things like the Lorenz contraction actually predate Einstein. Sure instead of one genius developing the whole theory in a single paper, it might take several people up to a decade. But it will happen.
And nuclear physics development is completely independent of Einstein, anyway, up until fission is seen (and the amounts of energy it releases can be calculated).
Delaying a Bomb past *WWII? Easy. Delaying one past, say, 1960 gets tough, and every decade after it gets exponentially more unlikely.
So. No.