I seem to recall you need SSH 3.1.x or higher. Also, generally speaking, if you want to do port forwarding then you should be using Oracle Connection Manager (CMAN) on the same server as your Oracle database. Even still, Oracle's Enterprise Manager client version 2.x may continue to fail as it is not supported in port forwarding environments.
Back in Oracle 734 we could not run MTS (now "Shared Server") through firewalls that performed port forwarding - not sure if that's still an issue or not.
Oracle's MetaLink web site has lots of info on configuring SSH for specific products like Oracle Data Guard. Maybe they have some articles to help your office too.