I don't disagree with the OP's basic premise -- that the Stuka was the original German tactical bomber, and indeed served through most of the war -- but the issue is also moot since we really don't distinguish between the capabilities of the units in the tech trees of different countries. In Call of War's level of abstraction, there is in fact only one tactical bomber that is shared by all in-game countries and its combat characteristics are only differentiated by the level of research completed.
So, yes, we should add the Stuka to the German tech tree for the sake of historical reference, but let's also acknowledge that the practical consequences of doing so, given the game's level of abstraction, is meaningless.