Go is not really a "Google" technology. It's just a programming language like any other. There's no reason Apple shouldn't use it, if it's the right tool for the job.
Actually, google does a lot of iOS development and has dozens of shipping iOS apps (https://itunes.apple.com/us/artist/google-inc./id281956209), and thus has a pretty sizable community of Objective C programmers. So Google will almost certainly be shipping apps containign Swift code as soon as the tools stabilize enough for them to do so.