Better not be. If there is an OTA feature then I hope they can let you update and then your iDevice would become unusable because there is no reason someone without a registered UDID should be on it.
Wait, what? If you OTA update from iOS 6 Beta 1 to iOS 6 Beta 2 it should work, because it is a delta update. So it just updates the broken things, not the whole OS again, so you wont need to go through the First time setup, so your device won't look to see if your device is activated.
It probably will be, but, as you may know, it's incredibly simple for Apple to make it so that you cannot update without registered UDID. Just needs to reload the setup.app preference file (reason why unregistered users are on it now)
When you go to the Software Update page, it checks your SystemVersion.plist to see if you are on a beta. If so, it will check for beta updates as well as standard updates.
So does that mean that you could technically be on iOS 5.1.1 and change it so that it can see beta OTA Updates, then OTA update to iOS 6 Beta 1?