This is an interesting question that hits on one of Harper Lee's major moral points in her novel:  people are their actions and kindness, not their backgrounds.  Take for example the contrast between Bob Ewell and Tom Robinson.  Both come from backgrounds that, in their town and society, were considered a bit shameful and disgraceful.  But, Tom Robinson is a decent, hard-working, loving, polite, moral man whereas Bob Ewell is immoral, lazy, hateful, prideful and hypocritical.  The contrast here empasizes the moral that your background isn't who you are; your moral character is who you are.  Then, there is Boo Radley, who had been in court when he was younger, came from very stern and antisocial parents, and was a total social recluse.  Despite all of this, Lee focuses on his attempts at friendship with the kids, and his heroic and difficult rescue at the end of the novel.  He might have come from a strange background, but he did good things.  So, even though Dill comes from a broken home and is passed around from relative to relative, Lee focuses instead on his big heart, his vulnerability and his humanity.  She does this with every character in the novel, and uses it to enforce her conviction that who you are is determined by your actions, not your past or your background.