I really hate Sharepoint lookup lists. First the chosen item appears as a link in a view making it very confusing for users. And if a lookup item is deleted then that value is blanked for every item were it was the choice for the item.
Is there any way to use a list as a source of choices for a general choice control on Nintex forms?
P.S. I need to be able to do this from a repeating section.
I'm actually doing this same thing in a repeating section. I pulled it off by simply dropping a List Lookup in the repeating section. Make sure you name the control properly and it will drop the ID of the selected item in the generated XML for the repeating section. Hope this helps you, if you need more information I'll take a look at exactly how I did it.