Yes, you can install Oracle 9i on RedHat Linux 7.1, 7.2, 7.3, 8.0, 9, Red Hat Advanced Server 2.1, and on Red Hat Enterprise Linux Advanced Server 3 (RHEL AS 3) even they are not certificated. Below is a good website to address most of Oracle installation problems on Linux.

http://www.puschitz.com/InstallingOracle9i.shtml