iOS: Distribute beta apps without UDID
TestFlight do not require UDIDs any more. You can distribute apps with TestFlight without having the UDIDs of all those test devices. Just invite the testers by providing their email addresses. They will be able to join you. You need an Apple developer account (99 USD per year) to use TestFlight.

And yes, with Developer Enterprise Program (299 USD per year), you can also distribute enterprise apps. You can distribute such apps to the users directly by just providing the Email address, and have them installed on the devices without any limits. Enterprise account does not require UDIDs. Know more about TestFlight, Developer Enterprise account and other options at Enterprise App Distribution - Hexnode blogs