Has anyone created a field with serverWidget that would allow a user to either upload a CSV or select one from the file cabinet? I'd be curious to see how this works.

You can definitely do it w/ HTML and the input of type file. Not sure if you've done it that way or not

you mean an HTML form? i was hoping to do it with a NetSuite field.

yeah html form. There IS a file field type for ui/serverWidget though