Forgetting about Iscsi, I went to try to enable RSYNC to /from ESXi.
I enabled password-free SSH on the ESXi server and downloaded the self-contained rsync executable from http://computerpr0n.com/2011/04/esxi-remote-management-part-2/. I then created merged 2 rsync scripts, the one from the blog above and the one from http://troy.jdmz.net/rsync/index.html, in order to create one that runs without password-prompt to synchronize a local ISOs directory on a Ubuntu machine and the ISOs datastore on ESXi. It works perfect and allows me to have the files I need on ESXi for my VMs as well as a local backup. The final result looks something like this:
rsync -avr –delete -e “ssh -i /esxi-key/esxi” –rsync-path=/vmfs/volumes/datastore1/Others/rsync /my/local/datastore/ISOs/ user@ESXiServer:/vmfs/volumes/datastore1/ISOs/
esxi-key/esxi is the path where the SSH keys shared with the ESXi server are hosted on the local machine
/vfms/volumes/datastore1/Others/rsync is the path on the ESXi server where to find the self-contained rsync executable
The rest should be pretty much self-explanatory after a standard RSYNC tutorial.