Currently there is an Action 'Send email from a Shared mailbox', however, it does not work for O365 groups. I have to use 'Send As' in regular send an email action.
It would be to great to add the functionality in Action 'Send email from a Shared mailbox', that it can also send FROM an O365 group mailbox.
We now released a new connector for Office 365 Groups mails (conversations). Unfortunately, Group conversations, while similar to emails, are different. You can find the connector here: https://docs.microsoft.com/en-us/connectors/office365groupsmail/