Elemental Damage on Ammy/Bracers

I don't understand how this works. I have a UE Multishot and GoD Hungering Arrow DH. UE uses cold % dmg on ammy/bracers and has cold as the elemental damage rolled on the weapon. GoD has fire on ammy/bracers/weapon. Neither variants use SoJ. Why is elemental best in slot and does the elemental damage on the weapon matter (I read it doesn't but that confuses me since the rolls on ammy/bracers always seem to match weapons dmg type). Please help me understand, I greatly appreciate it.