In my opinion, "supported" and "officially supported" are not the same as "fully compatible".
You are looking/hoping for compatibility and I don't see that mentioned. What I believe Polycom is saying is they will fix or attempt to fix what is broken (that is what support is). That does not mean that they have to incorporate features that Google doesn't offer.
Free GoogleVoice service is great, until it isn't. The lack of ability to turn off their automatic forward to voicemail is a feature many people want also that isn't going to happen.
I have both GV numbers,
Voip.MS numbers and CallCentric numbers. The last two because GV doesn't do what I want and I am willing to pay some other company for the feature.