Publishing HTML column

This is the column, that when Publishing for the site is turned, you can go to Site Settings, Site columns, and create a column of type Publishing HTML ("Full HTML content with formatting constraints for publishing"). If you create a list using this type of column and then create a form based on that list, the auto generated form will not include that field type. Also, you will not be able to create a column from within the Nintex form designer of that type.

Yes - it's a fact. In Nintex Workflow this column type is available. If you really need to use this special type of column within a nintex you can think about a Workflow copying the content into a multiline of text column for edit and another workflow to update the column itself...