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The release notes say it's necessary.
. If you wish to install Apple TV Software beta on your device, you must first register your device UDID in the iOS Developer Program Portal.

I have it on my ATV3 and didnt register it. Just did an OTA update a few days back and everything works fine
 
I have it on my ATV3 and didnt register it. Just did an OTA update a few days back and everything works fine

I guess you don't need it then. Did you register when you first installed? I was just answering based on the release notes. I don't have it installed since I am not interested in the beta for it.
 
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