According to this link et le Windows Server 2008 R2 Best Practices Analyzer, le loopback address should be in le list, mais never as le primary DNS server. In certain situations like a topology change, this could break replication et cause a server to be "on an island" as far as replication is concerned.
Say that you have two servers: DC01 (10.1.1.1) et DC02 (10.1.1.2) that are les deux domain controllers in le même domain et les deux hold copies of le ADI zones for that domain. They should be configured as follows:
DC01
Primary DNS 10.1.1.2
Secondary DNS 127.0.0.1
DC02
Primary DNS 10.1.1.1
Secondary DNS 127.0.0.1
