Displaying the Unique ID in the form

Are there any other widgets or functions that would do this?

You can try our Random Value Generator: http://widgets.jotform.com/widget/random_value_generator. Well, from its name, it gives you a random number instead of series. But you can display this in the form.

Here's how you can add a widget in your form: http://www.jotform.com/help/252-How-to-Add-a-Widget-to-your-Form. 

Thanks