Clarence Gilyard Jr. and Daniel Roebuck were series regulars together for all of season 7 and a few episodes of season 8 (when Gilyard left), but due to one or both not making an appearance in a given episode, they were only in two together.
No, he does not. While normally his client is innocent and the episode is about proving them innocent by finding who really committed the crime, that it not always the case. Normally, only once a season Matlock is shown to lose a case whether his client is really guilty or not. So while he wins most of his cases, he does not win them all.