My older version, located at http://lubi.sourceforge.net/unetbootin.html
(direct downloads still available at http://sourceforge.net/project/showf...roup_id=198821
you want the .sh version of the package titled "UNetbootin Ubuntu 8.04") was actually capable of being run from command-line, though I scrapped that functionality since essentially all the users were using the GUI version. However, no I did not implement automatic installation for it, since that would mean different install mechanisms for each distro (preseed for debian-based, kickstart for redhat/fedora, etc). However, if all that's important for you is that you can do it remotely, wouldn't something like X tunneling over SSH or VNC do the job, or maybe virtualize your install environment via XEN or the like and SSH into that?
FYI, if you wanted to prepare your own script to automate this (shouldn't be that hard, all you need to do is add preseed generation functionality to my older .sh version) see http://bazaar.launchpad.net/~gezakov...y97hfajhph9-17
you'll probably be most interested in the "tohost" install mode section. As for info on generating preseed files (which you can automate the installation and pass username/password/etc configuration with) see http://help.ubuntu.com/8.04/installa...eed-using.html
Also, since you're doing this on remote servers, I'd suggest simply setting up an FTP server and do a local FTP-install from that, rather than using an ISO file, you can find info about that at http://help.ubuntu.com/community/Installation/LocalNet
(you'll probably be most interested in the section titled "Advanced: Hands-Off, Preseeded Network Server Install")