The man page of cpio says:
...
  -c     Use the old portable (ASCII) archive format.
...

But you included a patch:
cpio-2.4.2-svr4compat.patch
that makes cpio behave differently:

    case 'c':       /* Use the old portable ASCII format.  */
      if (archive_format != arf_unknown)
        usage (stderr, 2);
#define SVR4_COMPAT               <===================
#ifdef SVR4_COMPAT
      archive_format = arf_newascii; /* -H newc.  */
#else
      archive_format = arf_oldascii; /* -H odc.  */
#endif
      break;

This way -c means the new ascii format.

So, archives made with the unpatched cpio (other unix systems, old linux
distros) cannot be read with the rh6.x cpio using just "-c".

For instance:
find path|cpio -ocB > /dev/st0  (done on other systems)
Cannot be read/recovered with
cpio -icBdum < /dev/st0
While it's ok if the backup is done on rh6.x itself.

I think you should at least update the man page to reflect the different
behavior.