This issue has already been reported, but I figured it'd be best to post here too for others.
Currently in the beta branch, using Index/Knuckles controllers on a hybrid setup(Oculus + Lighthouse) does not allow the user to take advantage of the new finger tracking system. It does, however, seem to work with Windows Mixed Reality + Lighthouse hybrid setups, so that's great! While I understand that hybrid setups are not an officially supported setup within VRChat, a number of users do currently use it for full body tracking on non-lighthouse headsets.
For Rift hybrids in particular, being able to use Index controllers in VRChat ontop of FBT is advantageous, as the Rift Touch controllers cause IR interference with any device tracking with lighthouse technology, even 2.0 devices(Rift users in FBT have much more frequent hip flyoff than other FBT users due to this). Because of this, I'd expect many hybrid-setup users to pick up Index controllers for that benefit, as well as being able to track their fingers.
Hopefully there's an easy fix for this, even if it's not technically a bug!
Edit for the sake of more information: As Index controllers currently are on Rift-hybrid setups, they are treated as Touch controllers within VRChat.