Even when user has 'bulkadmin' role, query says user does not have role - SQL Server 2012
You could have problems whereby the DC is not available, the user is actually a Windows group, or you could possibly have UAC issues. It may even be a permissions issue in AD as regards the account (run xp_logininfo 'RS\sqluser' and see if you get an 0x5 error).

I prefer to directly query the system tables to get that sort of information:

SELECT  1
FROM    sys.server_principals sp
        INNER JOIN sys.server_role_members srm ON sp.principal_id = srm.member_principal_id
        INNER JOIN sys.server_principals sp2 ON srm.role_principal_id = sp2.principal_id
WHERE   sp2.name = 'bulkadmin'
        AND sp.name = 'RS\sqluser';