That is correct. The "RAID" in vSAN is Failures To Tolerate (FTT). Let's take a small example of 1 SSD and 1 HDD each in a 3 node cluster. You can have a max of FTT = 1. A copy of the data will live on 2 of the hosts, and the third will have a witness. You can now have a host fail and still have quorum to keep the VM running. The way quorum operates is different between vSphere 5.5 and 6. See Cormac's post: VSAN 6.0 Part 1 – New quorum mechanism | CormacHogan.com
The only consideration of RAID in vSAN is whether or not to do passthrough or RAID 0. As the previous poster said, passthrough is preferred, but some cards will only support RAID 0. I don't believe there are any performance differences. However, if you have a card that only supports RAID 0, you should disable the cache. If you can't disable the cache, you should move it to 100% read as you want the SSD layer doing the write cache. The major difference is that when in RAID 0, a drive failure means you will have to down the server, remove the drive, replace the drive, create a new RAID 0 on the replacement drive, and then have vSAN reclaim the replacement drive. When in passthrough, you can hot swap drives.
Hope that helps. Thank you, Zach.
