This may help http://nintexdownload.com/helpfiles/nw2010/NintexWorkflow2010UserManual.html#Nintex.Workflow.SecuritySettings

Thanks, but it's still confusing.

Nintex have exposed the list through the user interface to work around the permission quirk described.To add/remove users as designers, the user assigning the permissions must be a site  owner or have Full Control access to the Workflows list.

I have test that with SharePoint Design Permissions, I can create a Nintex Workflow, Run one, Check List Workflow History--but I can't see the Site Stuff.  I cannot even check Site Workflow History. So obviously you don't have to have full control to do most Nintex--at least with a list.