In conventional terrestrial applications, the vast majority of problems are software-related (usually 99+%).
For planetary exploration purposes, the chances of there being a hardware failure is probably boosted significantly.
Redundancy is achieved by various means. Voting was used on the shuttles. Pair-and-spare are used on some proprietary earth applications. A "Cadillac" solution would be to use multiple vendors for separate missions. In effect missions from other nationalities achieve an approximation to this ideal.
A composite of some of these approaches is represented in Arthur C. Clarke's "Rendezvous with Rama," which incidentally appears to be in the process of being made into a movie.
I now see that the directory tree is for a real time control application put out by Argonne National Labs and called "EPICS", for "Experimental Physics and Industrial Control System." The web site is here.
Collecting information from the web, it appears that the Rovers are using "RAD6000" CPUs. These are are made by BAE Eystems and are based on the IBM RS-6000 RISC-like 32 bit processor architecture. The processors are radiation-hardened. Check this out.
From here the system seems to have a single 20 MHz CPU, 128 MByte DRAM with error recognition and correction and a 3 MByte EEPROM.
VXWorks OS images appear to be traditionally cross-compiled from Unix (Solaris, etc.) systems, so the directory structure of the build tree does not necessarily represent the directory structure of the live filesystem.
The RS-6000 architecture does not appear to be a standard Wind River supported architecture, so VXWorks might have had to be ported to it by BAE Systems in their BSP (Board Support Package)-- another potential source of problems if it was not done carefully...