Since WebObjects make use of JDBC to connect to the Oracle server, it is fully compliant with Oracle 9i and 10g (and 8i for the most).
Last year (2005), a quite huge WebObjects deployment (40 XServes) has been demoed in combination with Oracle 10g RAC (Real Application Cluster). Press release: http://www.oracle.com/global/eu/pressreleases/10gonmac.html
What was interesting is that the standard WebObjects deployment is clustered-like, and so is 10g in its RAC version. The performances and the load-handling were quite impressive.
PS: Would you like more info on WebObjects + 10g RAC, you are more than welcome to drop a question at http://www.intelli-core.com. Probably, your Oracle rep will welcome you, too ;-)