Can you configure Azure AD to trust another IDP than ADFS, yes >
https://docs.microsoft.com/en-us/azure/active-directory/connect/active-directory-aadconnect-federation-compatibility
Can you configure Azure AD to trust Google SAML (Assuming that it is a name of a product), no > Not in the list listed above.
Do you have to install ADFS on an ADDS server, no.
Do you need ADFS to work with Office 365, no >
https://blogs.technet.microsoft.com/pie/2017/02/06/do-i-really-need-adfs/
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