Do Constellar Delegates take extra chaos damage?
All of them.
Chaos is one of the so-called multi-school types and includes:
- Arcane
- Fire
- Frost
- Holy
- Nature
- Shadow
- Physical
So basically Chaos has all 7 schools and with that is the one with the most schools. Ranked 2nd is Elemental with just 3 schools (Fire, Frost, Nature).
So in that mentioned Argus encounter you're lucky.. All adds will take amplified damage from Chaos skills.