There really is no evidence in the story that can answer how Walter Cunningham feels about the trial of Tom Robinson. It is obvious that Mr. Cunningham doesn't even believe that Tom deserves the right to a trial, since his initial plan was to lynch him when he showed up with his friends to confront Atticus at the jail. Cunningham and his friends appear to be among those people who always take the word of a white man over that of a black man; yet, it is a Cunningham (though not Walter) who is the lone holdout on the jury. Atticus's brave stand in front of the jail, and Scout's innocent dialogue with Mr. Cunningham about entailments and Walter Jr. must have changed the Old Sarum man's mind. Scout reminded Mr. Cunningham of all that Atticus had done for him, and how Atticus had welcomed Walter Jr. into his home. This respect led him to walk away from hanging Tom and, possibly, even convincing his kin to support Atticus at the trial.
yes is isn't not.