Are AD Groups the exact same as individual windows logins with explicit permissions? Does any application requires a windows/domain login to be explicitly added to a SQL Server instance or by replacing the login with an AD group that belongs to the server and has elevated permissions I would achieve the same thing?  

To clarify, I am referring specifically to application accounts (In this case we have an account for TFS (team foundation services)) and not actual "users" accounts.  Will any application fail if they can't find an explicit windows/domain user on the server?
Microsoft's doc about Connecting Through Windows Authentication says:


  By using Windows Authentication, Windows groups can be created at the
  domain level, and a login can be created on SQL Server for the entire
  group. Managing access from at the domain level can simplify account
  administration.


There are no remarks about restrictions for apps when using a group instead of a login. Also, John F. Tamburo' article says:


  
  The group membership is used as a path to access; all activity is
  logged against the actual user's account.  sp_who2 and every
  auditing tool will show logins based on the actual end user; and
  DDL/DML changes will be audited to that user.  No more guessing who
  used the application's SQL login - It's gone!  For applications that
  run as Windows services, the service account under which the
  application runs is made a member of the necessary groups. (emphasis added)
  


So, as long as the group mapped as the SQL Server login keeps the needed privileges for the applications, no problem would be found on that change.