Instead of using FAT it is using a new format called VMFS-L. This new format allows much more and faster I/O to the partition.
This ESX-OSData partition is where frequent data is written and combines the product locker and scratch log partitions which were used in previous versions of ESXi.
This partition is more commonly seen as the /scratch partition.
The level of read and write traffic is overwhelming and corrupting many less capable SD cards.
The current versions of ESXi OS 7.0 Update 1/Update 2 are no longer throttling I/O to local boot drives.
The advanced setting to throttle I/O to local boot drives has been removed in 7.0 U1/U2
The version 7.0 Update 2 VMware ESXi Installation and Setup Guide, page 12, specifically says that the ESX-OSData partition "must be created on high-endurance storage devices".