Is there a way to send documents from a Site Collection to Records Center using Nintex Workflow?
This can be done with the help of the "Office 365 send document to repository" action. Please be aware that the "Content organizer" features has to be activated in the destination site.
A year old post, but might be helpful for others who might refer to it.
Office 365 Send Document to repository, up until now (11/4/2017), only works if the document and repository is in same site (It's by design, as they call). Below is what they have in official documentation.
Sends a document from SharePoint Online site to a repository (same site).
The best bet, at the moment, is just see if you can use OOTB information management policy to define a stage to submit documents to record centre.