Absorbed, but not always completely or correctly.
Countries where My System is considered standard reading still produce the most GMs - Russia (#1), Germany (#2), and Ukraine (#3). The USA is #4, and many of our GMs are from the former Soviet Union, and India is #5, where the hypdermodern style of analysis has long been preferred.
To suggest that players don't suffer without fully absorbing Nimzowitsch (or Tarrasch for that matter) flies in the face of substantial evidence to the contrary.
Both Tarrasch's and Nimzowitsch;s books are nearly a century old, and everything worthwhile in those books has been absorbed into common practice. The teachings of the Steinitz/Tarrasch school have stood the test time, and the the important contributions of the hypermoderns have become the common property of all strong players. The idea that there is some magical property in a book Nimsowitsch wrote mainly to try an attract a backer to finance a world championship is simply ridiculous, Many of the strongest players in the world have either never read "My System" or put it down without finishing it. And that doesn't seem to have hurt them