I don't understand. The blog post states that Microsoft is asking Google for permission to use the API for searching categories. Isn't that particular call available to anyone who signs up for a Google developer account?
This looks like the specific API for category https://developers.google.com/youtube/2.0/developers_guide_protocol_category_keyword_browsing
Why is Microsoft having to do anything other than fill out the same form to get a developer account that everyone else fills out?