Does openSUSE even use iptables?
It does, but the recommended (official?) way is to go to yast2->security and users->Firewall. There you can go to Allowed Services and click on Advanced. Create a new service, e.g. ED2K, and specify the proper ports, both TCP and UDP. Then select it in the "Service to Allow" tab and click "Add". That should do the trick.
I personally do not do this, I am used to have a script to tweak the tables myself, but the reason beeing that I do that since long before there has been a nice GUI to do the job. Also, I am not so fond of GUIs

Cheers!