Oracle rac does not support rhel5.x, rhel6.x, and rhel5.xrhel6. x.

Oracle rac does not support rhel5.x, rhel6.x, and rhel5.xrhel6. x.

Oracle rac does not support rhel5.x and rhel6.x

Because rhel5.x and rhel 6.x appear in oracle as "different operating system versions"

The answer from oracle's sr engineers is as follows:

There shouldn't be any problem in installing RAC with different patch bundle as long as they are meeting with minimum requirement.
Oracle does not support running different operating system versions on cluster members, unless an operating system is being upgraded.
You cannot run different operating system version binaries on members of the same cluster, even if each operating system is supported.
In your case, it is not a different operating system version so there shouldn't be any problem. However, It is recommended to have both the OS at same patch bundle

 

My supplement: The above English answer does not take into account the composition of the asm disk group (asmlib or raw ).

 

The difference between rhel 5.5 and rhel 5.8 is only the OS patch bundle. rhel 5.5 and rhel 5.8 share the same operating system versions.

 

Extended: For windows rac, for example, if one node is windows 2003 and one node is windows 2008, the other node cannot be windows.