I don’t relaly know how effective Rove was. Bush got 9 and 11% of the black vote respectively. And that was without a black guy as an opponent. If Obama, or some other black guy was running in 2000 or 2004, I doubt Bush would have done any better than McCain did with blacks. Conversely, if there was a white guy or Hillary running against McCain, he would have done the same as Bush did with blacks.
It was the black guy at the top that pumoed the numbers, not anything McCain or the GOP did.
As for Latinos, McCain is as pro-hispanic as you can get. It was the economy and the backlash over immigration that led to the drop, combined with the fact that Bush probably gained a bit from his time in TX and Jeb’s connections in FL. McCain actually did 8 pts better than Bush among Hispanics in CO for instance, and still lost because he did worse among whites.