Adding people from Intrantet to ASP.NET Roles

I am creating an Intranet website for an organization. I am using ASP.NET role provider to manage user roles. I have different ASP.NET Roles within the website. I am adding people in the Network just like the following example -
http://weblogs.asp.net/scottgu/pages/Recipe_3A00_-Implementing-Role_2D00_Based-Security-with-ASP.NET-2.0-using-Windows-Authentication-and-SQL-Server.aspx
Is it safe to add people on the Network to the website this way? Do I have to validate people against the Active Directory? Is there anything else I have worry when I add people this way? Thanks