(Assuming you've already found the com.mendix.core.Core.execute method for firing Microflows and the com.mendix.core.Core.create method for creating objects, both these methods will allow you to easily interact with the Mendix DSLs, i.e. getting information 'into' the Mendix database)
You can go two ways with this. Assuming your CORBA service has some kind of authentication in place, it could be perfectly fine to use the System Context for this purpose. Instead of setting up an entire session, simply use Core.getSystemContext whenever a context is required (firing Microflows and creating/committing objects).
If you'd like to have some kind of authentication or limit what your CORBA service can do, you can also manually instantiate sessions using the com.mendix.core.Core.login method:
public static ISession login(String userName, String password)
Whether you hardcode a user/pass in your service to limit the authorization of the service or add them as parameters to the CORBA service is up to you. Note that only one active session can currently be active for one user, so using the login method can introduce concurrency issues if the session doesn't persist in your CORBA service.