Dumbo is my favorite Disney movie. As for "racism" in Dumbo you can find much worse in other Disney movies. Seriously, google "racism in Disney movies" and you'll see how almost every movie is racist. Why does Tiana have to make gumbo instead of, say, pizza? Why is Scar a darker shade of lion than Mufasa and Simba? The beginning of Aladdin is blatantly racist. The Siamese cats in Lady and the Tramp are completely racist and then they used the same anti-asian racism in Aristocats. Little Mermaid is racist during "under the sea". Jungle Book shows black people as monkeys. Peter Pan has the most racist song I've ever heard. What makes the red man red? yeah, nothing racist about that!
I guess if you don't count Asians or Native Americans as a "race" then you'd excuse a lot of these portrayals. But as someone with Native American ancestry who adopted a Korean girl I find these anti-Native American and anti-Asian portrayals just as insulting as a black person would consider the crows in Dumbo.
I don't want to turn this into a racism thread, I just want to point out that if you're going to criticize my beloved Dumbo for being racist then you'll have to criticize like 80% of Disney movies. Maybe Fox and the Hound is OK.