Nello @nomadsrtw, Igor here, I just made some tests with the mailchimp widget and it works fine.
There is something important to keep in mind while using it:

1) Using the free version, you can only create 1 form template
2) If you use the form template provided by our demos, it’s made to stay in a row and not in a widget. You can edit the form in the Mailchimp form settings (more info https://wordpress.org/plugins/mailchimp-for-wp/)
Please look at this example that works in the widgets too: https://d.pr/free/i/Svb9lq
3) If you need to put the forms in multiple places like sidebar and contents, and you are limited by the HTML structure, you have 3 possibilities:

A) easier: purchase a license of the mailchimp plugin, and make multiple forms

B) find a second plugin to manage other forms, there are many free ones
https://wordpress.org/search/mailchimp#gsc.tab=0&gsc.q=mailchimp&gsc.sort=

C) Use the same form structure in widgets too, but of course the design requires lower expectations at it would require to use the same piece of code for multiple areas. In this case, the code provided in the example above will fit your needs.

I hope the solution can help you witht he project, if you need more help please let me know

regards
Igor