Most likely you are going to need to somehow retrieve the schema of the Oracle db and then hand-code your models to match. There are scripts that can help for MySQL and Postgres but I don't think that's going to work for you: http://code.google.com/p/web2py/source/browse/#hg%2Fscripts
You also need to pay special attention to "id" fields: http://web2py.com/book/default/chapter/06#Legacy-Databases-and-Keyed-Tables
