Thanks a lot!
I've got something workable now using the node.js library you linked. Your post was very helpful, as is your driver.
If any Googler is interested in what I'm going to be using to meet might needs, I'm using these modules:
tmi.js to read Twitch chat and detect which messages are channel reward redemptions
gamecontroller - this reads HID which is a bad way to do this in the long term because pressing LT and RT at the same time results in it thinking neither is being pressed. I couldn't find an xinput library that would build in Node 12. I'll migrate if I ever need LT/RT. I had to manually modify the vendor information to support xbox-like controllers.
node-ViGEmClient as linked by nefarius in his post.