That is just a Terms Of Service change away. Such legal changes aren't even unlikely: Google already changed their Terms of Service in the past to allow them to combine information from separate sites and services, which they didn't explicitly claim to do before[1].
The 'reassurances' provided in Google's Terms of Service don't mean jack shit when they have the power to change the terms in the future to whatever they want.
That would only work going forward. You wouldn't be able to merge the data retroactively.
And why would they do that is the question. Again, since they don't serve google cookies on analytics this would be virtually useless. An IP address isn't much to go on. Even a 5% misidentification rate would lead to horribly polluted data about users very quickly.
The 'reassurances' provided in Google's Terms of Service don't mean jack shit when they have the power to change the terms in the future to whatever they want.
[1] http://www.cnet.com/news/google-wants-ability-to-combine-you...!