I have a machine booting ESXi 5.1 on Intel 520 180GB SSD. Then then running FreeNAS-8.3.0-RELEASE-x64 (r12701M) on a VM that I have configured the 4 local 1TB 7200 RPM SATA disks as RDMs. http://blog.davidwarburton.net/2010/10/25/rdm-mapping-of-local-sata-storage-for-esxi/
FreeNAS runs ZFS on the 4 x 1TB (rdm) drives. I added 32GB vmdk on the SSD is used by FreeNAS as a ZFS cache.
NFS export list mount process requires the name resolution of the client. When a client initiates the request for a NFS share, the servers checks its export list for the requested directory and name of the client in this access list for that particular share. Now if server fails to resolve the name of the initiator it denies its request for mounting that share. In order to overcome this problem you must have a dns server in network or else you have you manually enter the names and IP address information in to hosts file of the server.
That little bit of news was very helpful during this build as I had not been able to connect from the ESXi host to the FreeNAS VM running on that same host after much tinkering with permissions and network settings. Opened up the console on the FreeNAS VM, edited /etc/hosts to give the ESXi server IP a host name. BAM, NFS mounted with no problem.