The Formidable Forms plugin includes reCaptcha module (both in Premium and free version). That captcha works with Hustle and PopUp Pro popups only if the popup is triggered "immediately". In both plugins, if the popup is triggered on click, "time activated" (e.g. trigger after 5 seconds) or on "scroll" - basically, on JS events - the recaptcha fields don't show up. However, if you try to send the form, there'll be a captcha error.