I believe Oracle can use OleDB. Also, I know Oracle has a .NET provider as well. I know it comes packaged with SSIS 2008 and I believe it comess with 2005 as well. If it doesn't, you can probably download Oracle's .NET provider from Oracle's site. Then, once you install the provider, it should show up as one of the providers in the Datareader Source Connection (2008 replaced this the ADO.NET source connection). You should then be able to replace all of your existing source connections with the DataReader source using the Oracle's provider.
One thing to keep in mind (I've seen this happen in conversions); when the files are converted from DB2 to Oracle, your DBAs may also update datatypes to the ones they feel are the most efficient in Oracle. This could be added work for you as you may have to perform data conversions in your package to compensate.