I second Kevin's recommendation - you could run centos or RHEL as vm on esx, to export nfs shares backed by nimble volume. XFS can be used as oppose to ext4 as it provides higher scalability. And vSphere HA provides simple HA for the vm.
Hi Alex, I've used SoftNAS since the day it was released. Very solid product, granted I've only used it as a basic CIFS fileserver with AD integration. I run the VMware version within our UCS/Nimble vSphere environment.
I would say try them both and see which one you prefer. In terms of compatibility, there should be no issue since they are virtual appliances. How many users will you be serving and how much data are you hosting?