It’s worth noting that a Google “Hangout” is not the same as a “Hangout-On-Air.” A Hangout-On-Air is streamed and recorded via YouTube in real-time. This gives it the potential for much greater reach. A normal Hangout is not streamed in this manner, although it does allow for PSTN connectivity.
This difference is arbitrary, although I’m told it stems from legal concerns about copyright issues that could easily occur if Hangouts-On-Air were allowed to have broad interop capability.
The fact that the VUC uses a Hangout-On-Air has compelled my search for a reliable, high-quality means of interconnecting the Hangout-On-Air and ZipDX conference bridge. Given my long-standing and vociferous support of HDVoice even the PSTN access provided by a plain vanilla Hangout is troubling. Connecting via a pure IP means, like SIP URI, would allow interconnection with much better audio quality.