Hello @ajj81,
There are some flows in the Center of Excellence that will send out emails (and Teams notifications). You could use an account from your primary tenant to create the connection to Office 365 Outlook. Please note that there may be restrictions in doing this if cross-tenant isolation is activated.
Why don't you assign an inexpensive license, say one of the M365 F licenses, to the admin account in the secondary tenant, though? This would probably make everything easier.
Also, some CoE flows will send out emails to the owners of flows and apps, e.g. to check for compliance. If your app makers are not mail-enabled in the secondary tenant, these mails would get lost.
And if you are using Power Apps in a secondary tenant, why not assign the licenses in this tenant?
I'm asking these questions because I think the setup you sketched above is going to be rather complicated and hence fragile to support in the long run.