Hi Marcel,
You do not need any license to use the Transports. As an existing Ariba customer, either you can log into your basic or DSC account on connect site and under the products tab (i.e. Procure to Pay or Procure to Order as whatever you have licensed for) you can find ABAP Transports for SAP integration.
Also you can directly contact to your respective Ariba support and ask their support to provide you with the transports.
Thanks,
Sandeep Jain