Opened an SR by support and got the following answer. Erasure coding is supported, you just have to ensure that there is a minimum number of fault domains to ensure availability.
Hi,  I was wondering if it's possible and supported to change the default VM storage policy for the VxRail manager. By default the "Marvin-System-Storage-Policy" is applied to the VxRail manager. I will feel more comfortable when the failure tolerance method is set to RAID-6 erasure coding with FTT=2.  Cheers!
VM storage policy VxRail manager