Reply To: Membership Plugin Compatibility?

Without being able to have a play and look at your files, I don’t really know.
But every theme uses PHP pages, and you can find them at WP admin > appearance > editor. I would think that once you create a Ultimatum template, that is where it goes.
Using a widget, you still would need a separate template for your profile page, or the widget will be on your other pages too?
You should be able to use http://wordpress.org/plugins/php-code-widget/ but exactly how might require a bit of experimentation …

PS: I am no expert but have learned a fair bit over the years mainly from fixing my own mistakes, advice given at your own peril 🙂