Exchange 2003/2010 2003 AD to 2008 R2 AD

Setup:

DC's

2003 - 2, 2008 R2 -1 Domain functional level is Windows 2003.

Exchange

1 - 2003 SP2 running Exchange 2003, 1 - 2008 R2 running Exchange 2010 SP3.

All mail comes in through the Exchange 2003 server.

Question:

Both of our 2003 Domain Controllers are in bad shape and need to be replaced. We are going to replace them with 2008 R2 domain controllers. Can we change the domain functional level to 2008 R2 and leave the Exchange servers alone or do we have to remove the Exchange 2003 server as well? Thanks for any help.