Yes, it is working for me. However, to get speeds of > 900 Mbps when connecting through the Studio Display I had to buy Anker’s expensive USB C to 2.5 Gbps Ethernet Adapter. You might be able to use a slower Gigabit adapter in the future if the firmware is updated.
My Studio Display is still “processing”, but there are issues with some ethernet adaptor chipsets that may result in reduced speed. One of the more recent ATP podcast episodes had some discussion about it, but as @bx987 mentioned, the Anker 2.5Gbps adapter doesn’t seem to suffer from the issue.
One thing that I have noticed with my current config (running 14" MBP though Thunderbolt dock with ethernet, moving between docked and undocked without shutting down), is that when I plug back into the dock, the wired ethernet adaptor resumes its place at the top of the active interfaces in System Settings, but until I turn off WiFi for a moment or two, the network traffic continues to use the WiFi interface.