If a juvenile is not required to register as a sex offender in the sending state, but is required to register in the receiving state, do I enter them into UNITY as a juvenile sex offender?

Yes; the ICJ Rules define a juvenile sex offender as “a juvenile having been adjudicated for an offense involving sex or of a sexual nature as determined by the sending state or who may be required to register as a sex offender in the sending or receiving state.” Therefore, the juvenile is entered into UNITY as a sex offender.