I recently installed squid on a RH6.1 server from the rpm on the CD. It
installed into /usr/lib/squid (Which I think is a really dumb place for it,
but anyway). The owner/group by default is root/root. But squid runs as
nobody, so it cannot create the cache directories on the first run. I did
notice this in an earlier version squid (not installed by RPM) so maybe it
is their problem, and not yours. Just thought I would mention it.
The default cache_dir is /var/spool/squid, which
is owned by user squid/squid. I can't reproduce
your problem here.