Well... looking at the screenshot you posted, ethminer is reporting 0 hashes/second on the console, so the UI will do the same.
Maybe give it a few minutes for the DAG file to initialize on each GPU.
This has to work, as it passed benchmark, and a real hashrate was loaded successfully (otherwise the UI would have never picked/used that miner to begin with)

Now that I figured out how to add additional miners, I'm very interested in adding the best-in-class miners/versions to this application.
Any suggestions based on experience? which miner should I add next?

Unfortunately, I sold all my AMD GPUs, so it's going to be hard/impossible to add and test AMD miners, but I have a couple of Nvidia 10XX rigs.