So, Ultra Japan is live streaming here, via YouTube:
https://ultrajapan.com/
For the first 2 days, they've been broadcasting mostly from the Main Stage, but they've had one headline act from the Live Stage (Underworld's stage) each day. So, I'd say there's probably a 50/50 chance that UW might be streamed tomorrow.
The Day 3 streaming schedule should be posted in about 16 hours here:
https://twitter.com/UMFTV