If you want to use the most recent version of 9i (Release 9.2) then certified platforms are (from MetaLink 'Certify and Availability'):

UnitedLinux 1.0
SuSE SLES7
RedFlag DC Server 4.0 (China-HongKong only)
Red Hat Enterprise Linux AS/ES 2.1
Monta Vista Carrier Grade Linux 3.0 (Embedded)