Yes, the G3’s remote will be able to adjust the volume on the Sonos Arc.

The Sonos Arc will be connected by HDMI to your television and volume adjustments from the remote will be carried over HDMI-CEC

I have this configuration now. (I just boutght LG G3 last week) and the volume control with the LG remote does not work for the Sonos on HDMI/ARC. However, my Apple TV remote DOES control the volume.

Any suggestions for fixing this? I hate using 2 remotes.

UPDATE - All is working now. I spent hours on the phone with both Sonos and LG support and messed with all kinds of settings. I reset and updated my  Apple TV 4K box and left it disconnected. I powered off the TV and the Arc. I then turned on the TV and attempted to do the TV setup for the Arc through the Sonos app. Every time I tested it failed. So I simply turned the TV settings to use wired HDMI (ARC) - HDMI 2.

The I set up the Apple TV 4K again on HDMI 1. I went back to the TV Device Controller settings and got it to recognize and “setup” both HDMI ports to recognize Apple and Sonos devices. After this config change the Arc (and surrounds) are now working with the TV and the Apple TV box and using the LG remote for volume control - even though it is a RF and not IR remote.

Go figure. LG and Sonos support were useless to me. (BTW - BOTH did remote to my devices to work on this, consuming many hours.)