Usine can receive synchronization information directly from/to a device.
In Reaper we simply select and activate MIDIYoke 1 as MIDI out device and we activate the MIDI Clock option:
Back to Usine, we activate MIDI Yoke 1 as MIDI input in the setup/Midi tab
That’s all ! now Usine receive tempo change from Reaper. Do the same procedure with a MIDI out device if you need Usine as master.