I was wondering if plugins like betterloot or any addons on umod that can support customization in crates for oil rigs, npcs, and harvesting of npc? Are these all supported or do they remain as vanilla atm?

Crates on OIL rig have same crates (and loot) as on any Radtown.
There are no free plugins to handle NPC loot

Hey!
I will work on Loot Plus soon and add this functionality I guess (at least radtown selection, but will think about changing NPC loot - also useful).