From the Certified Platform Tables, it says:
"All minor releases of a certified OS version are supported with the assumption that OS vendor maintains binary compatibility. For example, if Tuxedo 12.1.1 is certified on RedHat Enterprise Linux 6.1, RedHat Enterprise Linux 6.x are supported with the assumption that RedHat will maintain binary compatibility among all minor versions of release 6."
So RHEL 6.4 would be supported.
When you ask about interoperability issues with Tuxedo 8.1 client with Tuxedo 11gR1 server, it depends upon the type of client. All non-native 8.1 clients will work with Tuxedo 11gR1. Native clients won't work because they would need to be recompiled and relinked.
Jolt should support whatever version of Java you are using with WebLogic Server 10.3.
Oracle Tuxedo Chief Architect