Microsoft does not support your decribed configuration.
In a hybrid environment, you are required to setup at least one Exchange Hybrid "Management" Server to be in a supported environment.
afaik, this one is free, so you don't pay an Exchange Server license for that, but a Windows Server license..
That said, I've also got acknowledged, that using ADUC or ADSI you could manage your users this way. But, bear in mind, Exchange control panel and Exchange powershell do way more than just putting values into properties. Those are verifying attributes and values, checking for duplicates where neccessary, ...
I hope this helps a little..
Azure AD Connect with existing 365 tenant and local AD that had exchange removed before
Our company used to have a single exchange server but it was removed while at 2003. After this Active directory was upgraded from 2000 and then 2012. With all msExch.. attributes in active directory (I believe the schema is extended in 2012 even if there was no exchange server) does all these attributes have to be matched before sync????
For example, the msExchMailboxGuid is "not set" on my local directory, so if this syncs would that not break exchange online, since that "not set" attribute would over write the cloud?? What about all other exchange attributes?
I realize that smtp email addresses, and principle names will need to match, but I am currently concerned about the exchange attributes..
also, I plan to only sync selective accounts, and will likely not sync groups or try to match that. Then when I want to make sure users are part of exchange groups, will I be managing all group memberships in the cloud, or will I also have to managed attributes in local AD to make sure users are part of distribution and other types of office365 groups??
Finally, reading some old articles, its stating that MS does not support Azure AD connect sync unless an exchange server is in local premise for management. I don't plan on adding an exchange server to the local domain, but would manage attributes with the Editor in ADUC or using ADSI EDIT. Is this a supported method with Microsoft?
Thank you for any response.