Answer
Yes, but note that the HR Calendar and the Work Time Calendar are two separate, unconnected calendar structures — adding a holiday to one doesn't affect the other. To add holidays specifically to a Work Time Calendar, add each holiday date as a 'Schedule Exception' entry on that calendar, specifying it as a no-work day (or any other altered working hours for that date, if it's a partial-day exception rather than a full holiday). After adding schedule exceptions, you need to regenerate the calendar for those exception days to actually be reflected in its generated working-time data — simply adding the exception entries alone doesn't retroactively update an already-generated calendar.