My question is two fold. First is it possible to leave roles such as DHCP and DNS on a dcpromo'd out 2003 server and use only 2008 R2 servers as DCs? In other words, while in the process of upgrading, can we raise the domain functional level to 2008R2 while those functions...DHCP, DNS are still running on old 2003 Servers that are no longer DC's.
Part 2 - If that is not possible, is it best to split the scope temporarily between the old dc and the new 2008R2 dc before migrating with the Windows Server Migration Tools or just attempt the migration overnight?
Thanks in advance for any advise.