There is a "Dungeon Chests" loot tab, but how can you get loot pools from other mods to show up?

What other loot pools are do you mean? In general the idea is that mods register their own stuff to show up in JER.

I'm not seeing any of the loot_table from any of the mods being displayed by JER. The only values I'm able to find are from the minecraft/loot_table/chests folder. If I make a datapack and add more .json files to that folder, they still aren't picked up.