Link onpremise domain to Cloud Exchange using Essentials Role, compatibility with domain functional level?

Hello,

We have migrated our clients to Office 365 using Cloudmail of Microsoft (onpremise Exchange 2003 Server was shutted down).

Now our problem is that we want to link the Cloud to our existing domain.

We found that the Windows Server 2012 Essentials Role could be used for this.

With a patch that was released a few months ago, we saw that support was added for a system that has more then 1 domain controller. Our system has 3 domain controllers running on Windows Server 2008 R2, functional domain level 2003.

Will this work with the Essentials role, or do all domain controllers need to be Server 2012 with Functional Level 2012?

Thank you.

Joris