No, a subregistrar do not have agreements with registrants. The agreement for .se and .nu domains is entered into between the Registrant and your Registrar. You must always state this clear to customers.
Updated 29 May, 2020
The Swedish Internet Foundation is an independent, business-driven and public-benefit organization. We work for an internet that contributes positively to people and society. We are responsible for the internet's Swedish top-level domain .se and manages the operation and administration of the top-level domain .nu. The revenue from our business finances a number of initiatives in order to enable people to use the internet in the best way, and to stimulate the sharing of knowledge and innovation with a focus on the internet.