No, the A&S admit rate was 14.8% last year while overall combined was 15.1%, you can check it out yourself on their nifty web tool here.
Between Vandy and Dartmouth it's going to depend on what's strong about your app more than the couple percent difference in accept rates, with the former more heavily favoring high SAT/ACT scores.
Cornell is known for being rigorous/deflating for sciences, in contrast to Brown the great inflator. Dartmouth and Vandy aren't particularly famous one way or the other, but really there should be a clear preference for you between them unless you're totally indifferent to living in a city in the South vs very small town far in the North.