With Enterprise Distribution:

 - You don't need to include UDIDs in your provisioning profile; any device can install the app
 - You must host the IPA somewhere and provide an installation page (could be just a simple link)
 - Apple can and will lay the smack down on you if they suspect you are circumventing the app store

If you're not using an Enterprise profile, you have to manually collect and include UDIDs of the devices you want to allow in your provisioning profile. This is generally what you do for beta testing an app prior to release.

Long story short, I think your focus on a private Appexchange listing is misplaced. The first question you should answer is whether you're going to list your app publicly on the Apple app store, and if so, why bother with Enterprise distributions?

Enterprise Distributions are intended for apps internal to a single company, as the name suggests. They are not intended for distributing a private app outside the Apple app store.