Technically yes, developer credentials are not required to activate the iOS 5 GM.
However, being a developer, I recommend not installing it unless you are sure you know what you are doing:
- You need iTunes 10.5 B7, not B9. B9 is for testing iTunes Match. Attempting to activate the GM with the wrong version can be catastrophic.
- iOS 5 GM must be a restore, not an upgrade. The SKU for the OS is different, and they want future OTA updates to work. That is also the reason that he GM can't be installed OTA from the iOS 5 Betas
- Once you install iOS 5 GM, you can't downgrade. So, if you don't like it or it breaks some of your apps that haven't been upgraded for compatibility, you'll be stuck with iOS 5 till its official release (not too far away, but still)
That being said, there are no technical restrictions from installing iOS 5 GM on non-dev iPhones.