From my understanding, US diplomats are very much unofficial spies, as the US State Department keeps incredibly close tabs on all foreign governments. Allied or not, and enemy.
If I remember correctly, a majority of the CIA cables that were leaked - the ones concerning personalities and assessments of foreign government officials - were mostly generated initially by State Dept.
The US may actually be happy if we had GAC do something similar with their own assessments, and share them discreetly via 5 Eyes.