I will have a look when I'm online later but can you instead use a web service call to lists.asmx to create the item? 

I've thought about that as a work-around but was hoping it would be more straight forward like it is for everything else. Funny I can create a list or even a site from a UDA but not a simple list item? 

You should have the Create item in another site action.  You can use that one, and just leave the site as the current site. 

I don't see the option to create any item. I can Copy or Update even delete but not create? It seems wrong. These are the options I get under List/Library Actions.

What version are you using?

You may want to check with your admins to see if they may have disabled the action.  

Nintex Workflow 2013 (3.0.7.0) 

I am also a system admin. I did double check manage allowed actions, but I can see it is enabled (as I suspected because I can create an item from a Site or List workflow just not a user defined action). Unless there is someplace to enable actions specifically for UDAs that I am overlooking?

ETA: However in CA I did find the Create Item in another Site! And it does show up in UDA! Thanks so much. Getting things to format for the Web Service is such a pain!

You do not have the following workflow action (in red circle) when creating an UDA?

There is indeed no 'Create item' workflow action when creating an UDA workflow.

I found it - it was turned off in CA as this farm only has one site we never had a need to turn it on.