Should a SQL Server DBA know Windows Server and vice versa? Are these roles soon to become synonymous. Or at least more encapsulated/?
As a database administrator, you are part of a team whose goal is to make a job easier, or just possible, for someone. The team includes system administrators, database administrators, database programmers, application programmers, network administrators, and so in.

A valuable team member knows not only their own role but a little bit about every role in the team.

Specifically, as a database administrator, it will help you to know some or all of the following.


How to create and modify Active Directory user, group, machine, and managed service accounts.
What Kerberos Constrained Delegation is and how to set it up (including setting up Service Principal Names).
The basics of .NET programming (to help you talk to the application programmers).
The basics (and maybe the intermediates) of database design, e.g. normal forms (to help you talk to the database programmers).
Indexing (to help you get involved in database optimisation).


In addition, anyone working in an Active Directory environment will find it useful to know the basics of Group Policy.

As to whether or not you are better off being a "DBA who knows Windows" or a "Windows Admin who knows databases", that depends on the IT industry where you live. For example, I live in New Zealand (a country of 4½ million people). If you want to work in IT here then you have to be a "Windows who knows databases and email and terminal services and printing and troubleshooting and lots of other stuff." The industry is too small for specialists. :-)