However, there was a movie in 2004 called "White Chicks" which involved 2 African-American actors disguising themselves as white women, and portraying them as ditzy characters, and I don't think the film received any criticism for doing this.

The definition of racism is a belief or doctrine that inherent differences among the various human races determine cultural or individual achievement, usually involving the idea that one's own race is superior and has the right to rule others (according to Dictionary.com anyway). I didn't get any sense of alleged superiority throughout the skit, I think the whole point of painting their faces would be so that they closer represent the Jackson 5, similar to Robert Downey Jr.'s performance in Tropic Thunder.