Because of Front-End Difficulties--not mine, our SharePoint Server , our web service calls from within Nintex are not working. We are not even able to bring back the wsdl within the control--although the URL generated works fine if I use it in another tab.
Our processes need to do some SharePoint pumbling such as count and copy attachments, add attachments to lists and document libraries. The C# code is not that complex but understanding the connection within a workflow is.
I wouldn't know how to interact wiith one of these "APIs" directly, normally I would say "Create your own WebService and use whatever you prefer", but that doesn't seem to work for you either =\
There is a PowerShell action for Nintex: NTX PowerShell Action - Stable Release
I tried it out but were never able to get it running, maybe you are and it works for you as you should be able to do almost everything with powershell.