I don't actually get the IM or the notification on my phone. Strange.

In any case, 99% of the designers I work with and 75% of the developers have iPhone/Mac and don't use either Android or gchat although they all have gmail/google accounts. So if they got an email they would be notified, otherwise, they never know.

Without the link it is also really hard to just tell people to go to G+. The way to join the hangout if you don't have a link is hard to find

This is not just an opinion, like I said, I actually tried to set up hangouts several times and these are the reasons it failed. Just my experience.