With the Reaper setup, it suggests using the LogicTouch.osc or LogicPad.osc templates that come with the TouchOSC app. The volume control uses the automatic setting for the OSC message (eg. page 1, volume1 => /1/volume1 message by default). But Reaper has some OSC translate files, two being LogicTouch.ReaperOSC and LogicPad.ReaperOSC. In these files, it does the translation from the TouchOSC messages to the Reaper commands.
Yes, when Reaper is loaded with this OSC template and setup to send/receive messages to/from specified IP addresses and ports, and the TouchOSC layout is setup in the same manner, the volume levels in the layout immediately set to whatever it is in Reaper. As you adjust the volume faders in Reaper, the layout responds accordingly. Likewise if the layout fader is adjusted, the faders is Reaper move accordingly - just like in the X32-Edit app.