As per the SAG requirements document for wm9.0, Linux 6.0 is required/supported. However I have had no problems installing Wm9.0 on RH Linux 5.8 64 bit server.
Is any one aware of any issues with upgrading to 9.0 on RH linux versions < 6.0?
Since your using unsupported version, it may be problem for you in support call
SAG may point out this issue, better to upgrade your linux servers also