Nope. There is nothing that forces Googlers to either use or promote Go.
Well they ain't gonna use or promote C# are they?
If it's the best tool for the job, why not? They keep using and promoting Java despite Oracle suing their pants off over it.
Google is a very big and diverse organization, I'm sure there are some that do promote pretty much every language you ever heard of (and many you didn't).
Actually, I remember some years ago reading about some Googlers that used C#, no clue what for, and it was a while ago, but it is not unrealistic.