Does the installation of individual components of a SQL Server 2008 R2 (or higher) require a license for SQL Server?
Yes, Microsoft requires a SQL Server license for each machine on which a component of SQL Server is installed. This applies not only to the most current version of SQL Server, but as well to all previous versions up to SQL Server 2008 R2.
Licensing Guide_Microsoft_SQL Server 2008 R2 2016-07-27
Licensing Guide_Microsoft_SQL Server 2014 2016-07-27