I recently put a help sheet together to show how a Governor with a Hwb account can be added to an O365 group.
One way in which this is used by schools is to create an e-Safety O365 group to store evidence and policies for the 360 degree Safe framework. As a member of the e-Safety Group, the GB member is then made a member of the O365 Group, so they have access to the files and also to the conversation area.
The help sheet is here: Adding a Governor to an O365 Group