Oracle Access Manager for access via CICS/IMS and
Oracle z/OS Client for accessing via Batch.
I did some research a while ago and it turns out, Oracle has 'stabilized' its client software on z/OS. That's just a fancy way of saying 'we are NOT doing any maintenance to z/OS client' . Oracle 10gR2 is the latest and final version available on z/OS. However, this version is going to be supported indefinitely. Oracle 10 client is capable of accessing Oracle 11 database and future releases unless, Oracle changes its mind.
IMHO, such uncertain language is enough to deter any new applications from migrating to z/OS based access to Oracle and forcing current applications to choose between distributed Oracle or a native mainframe database like DB2.
If you must access to Oracle from mainframe using a more reliable way that will continue to be supported in future; look at Linux on mainframe or web service based access.