Figured out the graphing problem. /tmp/gengraphs.out showed that it was having exactly the same problem as the logging--unable to locate DBI.pm.
I added the following as line 30 to /opt/zimbra/libexec/zmgengraphs and restarted
Code:
use lib '/opt/zimbra/zimbramon/lib/i386-linux-thread-multi';
I've updated my first post accordingly.