Let's analyze the dependencies:
Red Hat 7.1 (Perl 5.6.0)
Requires:

    * ld-linux.so.2
    * libc.so.6
    * libcrypt.so.1
    * libdl.so.2
    * libm.so.6
    * libnsl.so.1
    * libdb-3.1.so
    * libdb.so.3
    * libgdbm.so.2
    * /usr/bin/perl 

Red Hat 8.0 (Perl 5.8.0)
Also Requires (in addition to most of the above list):

    * libdb-4.0.so (Only in RH 8)
    * libpthread.so.0 (Is already in glibc-2.2.4 found in RH 7.1)
    * libutil.so.1 (Is also in glibc-2.2.4 found in RH 7.1) 

libdb-4 can be found here for RH 8.0 (source RPM). It should rebuild cleanly on RH 7.1, but you should install it, rather than upgrade it (-ivh as opposed to -Uvh). This is the only spot that may cause you problems, since your current system probably has packages that depend on the old libdb-3, meaning it has to hang around, but the new libdb-4 might conflict with it.

If the libdb-4 source RPM doesn't work, you should download the latest Berkeley DB source from here. It uses GNU autotools, so should install in /usr/local... by default. Just add /usr/local...(whatever the library install path is) to your /etc/ld.so.conf and run /sbin/ldconfig as root to make the system aware of the new libraries before trying to recompile Perl 5.8.0.

Good luck,
Doug