I know for sure, as non United pilot, you can not jumpseat between Guam PGUM and Saipan PGSN or Guam PGUM and Hawai PHNL.
It’s all USA, one state, one territory, one commonwealth, but considered INTL as far as jumpseat.

Btw, captain can’t do anything about it, gate agents won’t even let you board unless they have a cabin seat available.