Its not necessary for hybrid environment. Ensure Exch 2010 is at the latest SP and Update
https://learn.microsoft.com/en-us/exchange/hybrid-deployment-prerequisites
AADConnect has to run on a 2012 server, but the forest level has to be only 2003 and above:
The Active Directory schema version and forest functional level must be Windows Server 2003 or later. The domain controllers can run any version as long as the schema version and forest-level requirements are met.
If you plan to use the feature password writeback, the domain controllers must be on Windows Server 2008 R2 or later.
https://learn.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-install-prerequisites