As I understand it, the Oracle Adapter is using a System DSN rather then the user id and password setting you put inside the adapter configuration.
I do not know if it is possible to have this dynamic – might want to try adding an additional field in the table and pass in the user id as a value (if this is possible).
If the Oracle Adapter doesn’t work for you, you might want to use simple .net call inside an Orchestration. You have more flexibility to pass in user id and passwords.
ESS could be used to store passwords and I think it could be used to do some type of validation but I have not used it enough to know if this would really help you. I don’t think you would have to use it in your scenario.
Hope this helps.