In Section 6.2.1 of the Installation Guide there is information on Native Components for Solaris and Windows. However, there is:
(a) no information on native components for RHEL (they also have 32 and 64 bit versions)
(b) no general information on what the native components are

The native components appear to be operating system specific libraries that provide information (at least) to the Administration Console. When booting without the native components installed a message similar to the following appears in the server.log:

"2009-12-15 15:02:53,112 INFO [org.jboss.on.embedded.ui.BootstrapAction] (http-0.0.0.0-8080-1) Initializing Administration Console v1.3.2.GA...
2009-12-15 15:02:58,362 WARN [org.rhq.core.system.SystemInfoFactory] (http-0.0.0.0-8080-1) System info API not accessible on this platform (native shared library not found in java.library.path).
2009-12-15 15:02:58,968 WARN [org.rhq.plugins.jmx.JMXDiscoveryComponent] (ResourceDiscoveryComponent.invoker.daemon-2) Unable to complete base jmx server discovery (enable DEBUG for stack): java.lang.UnsupportedOperationException: No native library available - Cannot get the process table information without native support"

It seems that native components provide low level information from the operating system that is not accessible from within the Java VM.