Yes, clemency serves as a safeguard in capital punishment, because it allows one last person to look at the case in its entirety. That person isn't bound by a rigid set of the law, and what their power allows them to do. Rather, they can look at the whole case and determine whether the exercise of clemency is fair.
I do believe that clemency serves as a safeguard in capital punishment cases, but I do not believe it is good enough. If a person is set to be executed in December of a particular year and they are not offered clemency, but new DNA evidence that proves the person was not guilty is found in January of the next year, that person would have no shot at clemency. While it is a useful safeguard, it is not an end all be all.