On cable it is, not on the DVDs. They even have a disclaimer somewhere in there. However, Johnny Quest oddly enough has this fate reversed, and it's a damn shame.
edit: I may have misspoken on Tom & Jerry, I'm referring to the supposed "blackface" cuts after explosions and such. I believe most of Mammy Two-Shoes' lines have been restored to the original voice on DVD, but wiki says some episodes contain the re-dubbed voice.