Hi @CP_INV,
If you mean shared Mailbox, currently it is not supported, there is an idea submitted on this already:
Office 365 Outlook integration with shared mailboxes
The status has been changed to Started, which I think it would be supported soon.
Besides, you may consider forward the Email from the Shared Mialbox to your own mailbox, which could be used under Microsoft Flow.
For group site, if you mean SharePoint team site, yes, it is supported, you should be able to choose the Team site by selecting the corresponding site address:

Please let me know if I have any misunderstandings.
Regards,
Michael