VMware ESXi always connects with root.
/etc/exports
/vol/esx_iso -sec=sys,rw=192.168.1.31:192.168.1.32,root=192.168.1.31:192.168.1.32 /vol/esx_swap -sec=sys,rw=192.168.1.31:192.168.1.32,root=192.168.1.31:192.168.1.32 /vol/esx_data -sec=sys,rw=192.168.1.31:192.168.1.32,root=192.168.1.31:192.168.1.32 /vol/esx_os -sec=sys,rw=192.168.1.31:192.168.1.32,root=192.168.1.31:192.168.1.32