It would be an exaggeration to consider O. Henry's short story a symbol of his anti-racism. His depiction of the the loyal old Uncle Caesar might even be called racist. The faithful black servant was once a slave of Azalea Adair's father Judge Adair and loved his white master so much that he continued to be practically a slave to the Judge's daughter.
The narrator, who represents O. Henry, is not as much of a die-hard Confederate and racist as "Major" Wentworh Caswell, but that does not make him anti-racist. He apparently regards Uncle Caesar as a lovable old rascal whose most endearing quality is his loyalty to his aristocratic white mistress. Uncle Caesar is what many contemporary African-Americans would call an "Uncle Tom." He not only works for Azalea Adair for nothing, but he actually gives her money to live on. In this respect he is depicted as a supporter of the old Southern aristocracy and the slavery that was the foundation of their defunct system.
One might say that Uncle Caesar enjoyed slavery and that emancipation meant nothing to him, since it didn't change his condition significantly. When "Major" Caswell has the audacity to appropriate the two dollars which Uncle Caesar extorted from the narrator to give to his mistress, the faithful old servant goes so far as to commit a murder for her. If he had been arrested and convicted, no doubt he would have gladly died for her.
O. Henry seems to be implying that this is the right spirit, this is the way that Southern blacks ought to behave now that so many of their former white owners have been reduced to poverty by their defeat in the Civil War. O. Henry's portrayal of the poor but proud Azalea Adair suggests a strong sympathy with the old Southern aristocracy and the system they represented. Uncle Caesar's unemancipated servitude to this lady helps her to maintain her illusion of gentility.