It depends on how you interpret the brother's motivations for wanting to teach Doodle these skills. The narrator admits that he wants to be proud of his younger brother, so the desire to teach Doodle the physical skills is a selfish one. When Doodle shows that he can't perform these skills to the narrator's liking, the narrator abandons Doodle to the rain storm and eventually, death. Therefore, I would conclude that the narrator was not a good brother. Brothers should love and accept each other for the skills and abilities they have and not try to change each other.
If the narrator's motive were more to make Doodle more accepted or developed as a person, I would say he would be a good brother, but since his motives are selfish, I don't think you can call him a "good" brother.
The narrator, Brother, is a good brother to Doodle. Consider that Brother could have simply ignored his handicapped brother and never paid any attention to him, even though his parents required him to take Doodle along. He could have just dragged the handicapped boy around, never really caring about him.
In fact, Brother pushes Doodle to fulfill his expectations for a normal brother, even though his motivation might be shame, he still puts his heart into teaching Doodle to walk.
"Driven by shame at having a crippled sibling, Brother forms a plan to secretly teach Doodle to walk. Eventually, he succeeds."
It is through this process that Doodle has his most wonderful experiences. When he is with Brother, Doodle is filled with wonder, love and admiration for his big brother.
Brother does not look at Doodle only as a handicapped child, he sees him in a different way, he sees potential even though he might have miscalculated Doodle's capacity. I think that he was a good brother overall.