Give users with Design rights full capabilities for Site Workflows
For SITE workflows, a user with Design rights to the site has limited capabilities to work with those site workflows. This is because they cannot see the Nintex Workflow 2013 menu from the gear/setting drop-down menu. If I send them a link to the workflow, they can edit it and publish it, but they cannot Manage Workflow Inventory, View Workflow History or Schedule Site Workflows since they can't get to the menu. To see the menu, they require Full Control rights to the site. We lock down sites so that very few people get Full Control rights to a site, so this is not conducive to delegating workflow management to power users. It would be ideal if these users with Design rights could also Terminate Site Workflows, but that's not as critical as the other functions mentioned above.
Reed Carr commented
One note, we got around this by having our users with design permissions go to Site Settings and use the Scheduled Workflows link in the Nintex Workflow section.