Glad you made it inside the Web Client. Maybe you can see at some logs in /var/log/vpxd.log when you try to add the device.
After sitting on the issue for a few days, I presented the issue to a few people that I know. One of them suggested re-initialising (setting the partition table for) the SSD while it was in the server, with a different OS. This was to see if there was a possible issue/bug with either the built-in storage array controller or ESXi/vCenter. I ended up initialising the SSD while it was connected to a laptop (GPT), which unfortunately destroyed the experiment. I then connected it back to the server, but also avoided sending it through the same setup as the other SAS drives in the server, detailed here. ESXi detected it, and so did vCenter. I was then able to add it to the virtual flash resource pool That was a bit of a ride, but now the info is here for others who may not have known before.