Yes AFAIK venet does need a static IP.
But I'd be interested to know what a 'normal' Ubuntu (ie non-TKL) OVZ template does. I'm assuming that this behaviour does not occur with them (or otherwise this wouldn't be a bug, it'd just be how it is).
I'm assuming that the line "/usr/sbin/vzctl set <VMID> --ipadd <IPADDRESS> --save" (see this post: http://www.turnkeylinux.org/forum/support/20120220/openvz-template-networking-issue#comment-12292) is meant to set the static IP for venet for the container but obviously it doesn't work with the TKL OVZ templates.
As I posted (http://www.turnkeylinux.org/forum/support/20120220/openvz-template-networking-issue#comment-12299) the Proxmox UI uses that command too, but first runs "vzcreate <VMID> --ipset <IPADDRESS>"... As I have no experience with vanilla OVZ I am unclear whether the "vzcreate" command is a generic OVZ command, or one supplied by PVE.