If anybody still interested. Checked the above rule and it did not actually let me access external resources being connected to the VPN server. I got connected to the server being able to ping external addresses this way, but there was no route to them through the VPN tunnel (when tracerouting). To be fully able to reach the external net through the VPN server I use the following:
iptables -t nat -A POSTROUTING -j SNAT --to-source <venet's IP>
And don't forget enabling IP forwarding in /etc/sysctl.conf: