 [solved]
Ok, I was able to solve this and all the other issues related to it in the cronjob by adding the following line in front of each command in the crontab:
LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/opt/zimbra/jdk1.6.0_02/jre/lib/amd64/jli
An example line looks like this:
10 * * * * LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/opt/zimbra/jdk1.6.0_02/jre/lib/amd64/jli /opt/zimbra/libexec/zmgengraphs >> /tmp/gengraphs.out 2>&1 |