I could not get the flashes to fire consistently from a Sony RX1R with the YN-E3-Rt
It's a Sony multi-interface hot shoe, but it will fire the 600ex-rt in the hot shoe.
The test button the YN-E3-RT fired them ok, and after doing that a few times sometimes it would work for a single flash triggered from the camera.
I will have to check the mode and try again, but I'm not optimistic.
You can try these things to help get consistent results.
1. fresh set of batterys.
2. make sure the yn3 is in M mode, not in GR.
3. Adjust the channels until it's reliable using the channel scanner on your 600rts.
I found ch.5 has worked best for where ever I've been shooting. I left my set there.