Running SSIS from a different server than the primary database instance
I would suggest reading up on SSIS at MSDN:
Initial Installation (Integration Services) -this references having a standalone installat of just SSIS.

Quote from above link:


  SQL Server Integration Services is installed through the SQL Server
  2008 Setup program. You can install Integration Services alongside
  other SQL Server components or you can install Integration Services as
  a stand-alone component. Integration Services includes both client and
  server applications.
  
  To use a dedicated server for extraction, transformation, and loading
  (ETL) processes, we recommend that you install a local instance of the
  SQL Server Database Engine when you install Integration Services.
  Integration Services typically stores packages in an instance of the
  Database Engine and relies on SQL Server Agent for scheduling those
  packages. If the ETL server does not have an instance of the Database
  Engine, you will have to schedule or run packages from a server that
  does have an instance of the Database Engine. This means that the
  packages will not be running on the ETL server, but instead on the
  server from which they were started. As a result, the resources of the
  dedicated ETL server are not being used as intended. Furthemore, the
  resources of other servers might be strained by the running ETL
  processes.


Some additional information could be found here as well: Considerations for Installing Integration Services. You might want to take under consideration the licensing as well and still validate the standalone server is licensed properly.