Need to know how to change ip address and hostname after deploying OVF template

I doubt that this will be possible with Equallogic, at least not without some downtime. The Equallogic architecture will allow you to change the ip-addresses of the interfaces without any downtime (provided the new addresses are visible to the old addresses) but the Group IP-address that is used for management and as the iSCSI target address cannot be changed without some downtime - once you change that you will lose connectivity to the entire set of arrays until you change the target settings on all of your ESX hosts and rescan. I would call Dell and ask them about this but I'd be surprised if it can be done unless they've added something new recently. If you do find out that it can be done, please let us know.

You might well be better off creating it as a full-stack install including the OS and all dependencies, on an OS that you know it works well under. Then let the end user decide if they want to install it standalone or as a VM guest on KVM, VMWare, Xen, or whatever. The only thing you'd gain over this with a KVM image is some amount of hardware-agnosticity, but there are still potential pitfalls there as you've pointed out, and the site would have to be willing and able to maintain a KVM host in addition to your application and its OS.

EDIT: To respond to your reformulated question, I think you've still go to leave this stuff to the sites -- VM guests, by design, cannot control how networking is set up on the host. You can certainly provide documentation and instructions for doing this in the simplest or most effective way, but that may vary from site to site. No matter what you do, if you distribute this as a VM image or appliance, the site will have to effectively set up and maintain a VM host that is specifically configured to work on their network.