It's a bit subjective depending on your definition of "continuous integration system".
For me, "system" includes the practice of the devs committing to and pulling from the working branch frequently. Given that definition, CDash is not a CI system.
However, CDash can be used as a CI server. In other words, it can continually check for commits to the working branch, and upon detecting a commit, run the project's test suite. This would form a critical part of the full CI system.
CDash is more than this though - it can receive test results submitted on an ad-hoc basis by devs, or it can run "Nightly" tests where the codebase is checked out at a given time daily and the test suite run.