Since OpenVZ is not a real virtual machine, but a Linux container, it is harder to support it.
Also, venet interfaces don’t have a MAC address which is necessary to make it work on NS 6.
You could try to use a veth interface to work around the problem, see also: https://openvz.org/Virtual_Ethernet_device
But @StreetGuru, you could try this command before installing:
chattr +i /etc/sysconfig/network-scripts/ifcfg-venet0
This will prevent the overwrite of network configuration.
Then after installation:
db networks set venet0 ethernet ipaddr <ip> netmask <mask> gateway <ip>
signal-event interface-update
Anyway you will probably experience some problems.
I hope the NS 7 will resolve this problem since udev does not relay anymore on MAC address to handle network interfaces.