At any rate, this question comes up fairly often because of that: "Can you run a SQL Server 2005 on a Domain Controller". The Microsoft's answer is basically NO but do it at your own risk (link).
The issues stem from basically how the SQL Service starts up in what security role.
Some key points of the reasons why they are against are;
- You cannot promote (dcpromo) or demote the domain controller's role after SQL runs. This basically means that you need to set up the DC and its role first before slapping on the SQL.
- SQL service must run on a domain acount and not on a local machine's system account or Network account.