Most of what the OS does is providing services for processes. Those processes call into the operating system from whatever cores they happen to be running on and the operating system generally provides that service by continuing to run on the same core. In addition, when the operating system has to dispatch later work, it does so using multiple cores.
This isn't a new feature. Modern multi-core machines are not all that different from older SMP machines that Windows has run on for years. Things like memory management and I/O were optimized because the Windows Server line would have been awful without it. Since Vista, Microsoft has worked significantly to improve the multi-core performance of features important to desktops such as graphics and sound processing.
So the short answer to your question is -- of course.