I can't see why not. RH 9 comes with UW IMAP. I have only used courier but squirrelmail can support both.
Just install the imap server from the redhat cd or download it here:
rpm -ivh imap-2001a-18.i386.rpm
Make the server start on boot then start it immediately:
chkconfig imapd on
service imap start
You can then download squirrelmail and configure it as neccessary (use the perl script conf.pl and you can set it to use the default options for a particular imap server):