A key factor is that you can only group zones using the same communication protocol. So all RoonReady devices can be grouped since they use RAAT.
The Bose outdoor speakers may use Airplay, which is pretty common. But understand you can’t group something that only uses Roon RAAT with something that only uses Airplay. It might be possible that some devices could use more than one protocol (my Devialet Phantoms do), so you could set up the device to work with the commonly shared protocol.
Roon supports Airplay, but AFAIK, Airplay2 is not supported. You may need to get the definitive answer from a Roon employee when they get to your post.