Not sure what you mean exactly by Windows CAL. If you are talking about the CPU/concurrent licencing required by Windows Server, then this won't affect Yellowfin.
Because Yellowfin is running independantly on Tomcat, windows licencing won't affect the way that this runs.
You may only have issues with licencing if you plan to connect Yellowfin to IIS. IIS concurrent users may be limited by the windows licence.
You may have to investigate this further.