No, the RTC UM can only work with a External 32KHz Crystal. Without a External 32KHz Crystal RTC component will not work.
When using a RTC UM the XTAL_32KHz option should be checked in the Clock Editor(like the below picture). Otherwise the creator will occur error “Error: mpr.M0063: The 32KHz watch crystal is not enabled and must be active for the one pulse per second interrupt to function. (App=cydsfit)” when building.