Got a raid 0 of 3 Samsung 950 Pro NVMe SSDs working on El Capitan 10.11.6 today. Previously, I was unable to get this working due to problems with the MinnowStor NVMe driver. With this driver there were a lot of write errors and issues with the appleRAID volume timing out.
Luckily Rehabman has done some great work and created a patch which modifies Apple's driver to allow 3rd party NVMe devices such as the 950 Pro. I highly recommend this patch as it worked for me and now I am able to create an appleRAID and get outrageous speeds.
View this blog post as well for more information about the patch.
I was able to achieve about 5600MB/s read and 3800MB/s write with 3 of the 512GB drives.
Everything feels incredibly snappy. Even Microsoft Excel loads in less than 3 seconds. Feels good!
Here is the PCIe x4 adapter card that I use with each of the 950 Pro SSDs to connect them.
You can purchase it on Amazon for about $20.