Allow db_owner to add/view existing logins to database
Isn't GRANT VIEW DEFINITION ON LOGIN::Whoever TO [domain\dbogroup] in master enough?
This is implied by MSDN (I think, can't test) in GRANT Server Principal Permissions 

Failing that, one quirk that may be useful for SQL Server 2005+

This may give no rows

SELECT * FROM sys.server_principals WHERE name = 'domain\somegroup';


But this will give a number if it exists

SELECT SUSER_ID('domain\somegroup');


Note: SQL Server 2012 has contained databases where logins are at the DB level