What do you mean by connecting?
If you're talking about using groups as a way to add people to waves, this is already done. You can add a Google Group to a wave and the members of that group that have Wave accounts will be added as participants to the wave.
If you're talking about message-level integration, where a message to a Google Group would appear as a wave, and a new wave will appear as a message in the group, I don't believe that's been done.
David