There are two ways to fix it without upgrading oracle.
A) Set up a seperate IS with older version of JDBC driver. (This will be an unsupported instance from webMethods point of view)
B) Buy a third Party driver from datadirect…
Considering that Oracle 7 is itself an unsupported version, why would the client want to run an app on it? It may actually be easy for the client to migrate the app (unless it is propriory code - which can work only on oracle 7) to a better version of Oracle or a different database alltogether - Say MySQL.