PhpMetrics seems to be relatively new. Does it use PHP_Depend or does it implement its own code analyzer? There is not a lot of information available on this tool.
As of now I use SonarQube as Continuous Inspection tool. In combination with Jenkins it is absolutely invaluable. SonarQube just needs the report XML files from PhpUnit, PHP_Depend etc. If PhpMetrics has an XML report file it should be possible to integrate it with SonarQube in order to have tracking of code quality metrics over time.