Copying Nintex workflows will make them available on the destination site.
You can copy list, site and reusable workflows. List workflows will be copied when you copy their associated list.
All the workflows from SharePoint version 2007, 2010, 2013, 2016, or Office 365 can be migrated to SharePoint version 2010, 2013, 2016, or Office 365 and will work at your destination.
Sharegate supports full migration of Nintex Workflows and Nintex Forms, from On Premises to On Premises for SharePoint versions 2007, 2010, 2013 and 2016, and full migration of Nintex Workflows O365 to O365, and will incrementally support migration from on-premises to Office 365. See here for more information.
Sharegate does not support Nintex Site Collection Reusable workflows since they are linked to Globally Reusable Workflows.
To migrate Nintex workflows, you can follow the procedure detailed here. Nintex workflows are copied the same way as regular SharePoint workflows.