
Hi Gert -
I'm not sure what the issue is with your configuration, but I can tell you that we're on XenServer 6.1 (hotfix XS610E030) with iptables enabled with VLAN-based advanced networking, and have no issues with connectivity.
chkconfig iptables off will only prevent automatically starting the service for specific init levels at OS boot... so if something is manually restarting it due to cloud config, chkconfig won't have an impact.
One thing that I've noticed is that if you need to restart iptables on the XenServer host, the rules do not get refreshed properly. The host itself does NOT store all of the rules required for use with CloudPlatform - some of the rules are dynamically populated when the server transitions to an "up" state.
My iptables file looks very similar to yours... however, if you run "iptables -L", you should see MANY more rules in the current list that are not in the configuration file - many of them configured for the bridged interfaces that CCP creates when you use advanced networking. I'd recommend putting the server in maintenance mode and rebooting it so that it grabs the correct rules configuration from CloudPlatform... then don't mess with iptables... let CCP handle it for you and see if that works.
K