Arguably, Abner Snopes may not have any redeeming qualities, whatsoever. It is not that he may lack them altogether, but that his bad qualities are so bad that they inevitably will end up overshadowing whatever good he ever brings out. For instance, the fact that he beats up his wife and children is the type of thing that leaves no room for any kind appreciation of his persona. Moreover, the fact that he is vicious, vindictive, and neglectful to his children makes his character even harder to connect with.
From Sarty's perspective as a ten year old, however, this may be different. This is because Sarty is still trapped between the world of make-believe that children idealize about their parents, and the creeping reality that is slowly looming over his view of the world.
For example, the deSpain mansion scene makes Sarty feels sorry for his father because of the treatment that Sarty gets from deSpain. Although this particular instance was completely propitiated by Abner, the fact that he (Abner) is belittled due to his lower social status may or may not lead the reader to feel sorry for him, and even to feel some form of agreement in Abner's want for justice in the form of burning barns as his revenge.
Yet all of that would still never compensate the wrong that he has caused society and his family as well. Just those two simple things cause enough damage to his character with very little chance for redemption.