If I was going to use autod feature of Set-HybridConfiguration:
Set-HybridConfiguration –Domains "contoso.com, fabrikam.com", "autod:wingtiptoys.com"
… which is now found in the GUI of the Hybrid Configuration Wizard…
As a hypothetical, would I need ANY DNS zones at all (either internal or external) for fabrikam.com or contoso.com?
Could they be non-existent with the exception of MX records externally?