These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
With the exception of Cliff Edwards, the voice actors were also black singers, the Hall Johnson Choir. All of them did a fantastic job on their song.
Fair for Its Day: See Unfortunate Implications, then consider that the crows are among the limited number of characters who are half-decent to Dumbo, and prove to easily be the most clever creatures in the movie.
I Am Not Shazam: Zigzagged; Dumbo's actual name is Jumbo Jr., while Dumbo was meant to be a cruel nickname. However, it's clear the name stuck, since he is always referred to by Dumbo by just about everyone, in the film or in real life.
The black crows, particularly the group's unfortunately nicknamed leader Jim. Generally given a pass despite the stereotype, for actually becoming helpful friends to Dumbo.
"The Song of the Roustabouts" is worse—it is sung by recognizably black circus workers as they pitch the tent and includes lines such as "We work all day, we work all night/We never learned to read or write," "We don't know when we get our pay/And when we do, we throw our pay away," and "Grab that rope, you hairy ape." To be fair, "roustabout" refers to any laborer performing temporary, unskilled work. The lyrics could instead be interpreted as the plight of any poor person in a labor intensive job, instead of being a blatant case of racism. It's just that the circus Dumbo was traveling through the Southeast during the story, and the labor pool in the area would be mostly African American.
The Woobie: Let's see... he's openly mocked and given a rather insulting nickname from mean lady elephants, gets the same treatment from some bratty kids, his mother gets sent to jail for justifiably attacking said kids (not to mention how much worse the attack from a fully grown elephant could (and should!) have been), he gets relegated to clown duty after getting stage fright on his first big act (which the other elephants denounce him for), and becomes accidentally drunk. He only has one friend to help him get through this, and said friend can't make everything better. When does all this happen? Over the expanse of probably about a week, starting from the day he's born. Dumbo just may be Disney's woobiest woobie ever, and you know that's saying something.
And his mother, whose sufferings we don't get to see, is kept in solitary confinement, unable to defend or even comfort her son through all these degradations, with the heavy implication that she's going to be destroyed at the end of the tour.