I don't really understand the outcome of this environment and all additional requirements for the system, but let me try to give some directions.

1. I think you can still use MSSQL tools, just make linked server to Oracle

2. You could create export scripts, CSV or INSTER, for batch processing on Oracle side.

2. You could use Oracle HS (heterogeneous services) which use ODBC driver to connect from Oracle to MSSQL, for direct processing

3. You could use (pay for) Oracle MSSQL Transparent Gateway which should provide (almost) 100% transparency from Oracle to MSSQL. This one should be used when there are some specific requirements which are not supported by ODBC driver

You have to give use some more details for the purpose of this solution.

BR,

Aleksandar