Hi jacob,
You can check you have libgcj installed on your box as a first step.
rpm -qa | grep libgcj
I too had faced libgcj dependency issue in amaozon cloud servers. i had used centos repo inside amazon and used to resolved libgcj
create a file /etc/yum.repos.d/centos.repo
Paste following contents.
[centos]
name=CentOS $releasever - $basearch
baseurl=http://ftp.heanet.ie/pub/centos/
5/os/$basearch/
enabled=1
gpgcheck=0
Do yum search libgcj it will list the package, after that you can procced with zenoss installation.
Thanks
Sandeep