In the watchOS Beta Software Installation Guide it reads:
Registering Your Device
Before installing watchOS beta software, register your device in Certificates, Identifiers & Profiles using the steps below.
1. Locate the Unique Device Identifier (UDID) for your device using Xcode.
a. Connect your device to your Mac and launch Xcode.
b. Open the Organizer from the Window menu and select your device.
c. Highlight the 40 character UDID string in the Identifier field and copy it.
2. Sign in to Certificates, Identifiers & Profiles and click the ‘Devices’ link under iOS Apps. 3. Click the ‘+’ symbol to begin the registration process.
4. Give your device a name and paste the UDID obtained from Xcode.
5. Click continue and confirm your entry to complete the registration process.
I'm assuming Apple means for developers to register the UDID of the iPhone, but not sure. Are they sayin that the watch itself has a UDID that needs to be registered?