VMWare ESXi NFS Oddness
I spent a good while debugging this not wanting to change too much incase it was something bizarre.
Turned out to be something simple.
Some posts on VMWare made me start me start to think that its something to do with permissions and I saw lots of references to allowing the root account and some people adding a root account to Active Directory.
This got me thinking, and I managed to resolve it in the end.