Chris, I do not understand what you mean by Transactional Templates. What I can tell you is that sending a triggered email within Wix can only be done if addressee is either member or customer.
If you don´t want that, you have 2 other options: sendGrid or using Gmail, Yahoo, Outlook etc using emailjs.com (read my article here: https://girizano.wixsite.com/codecorner/home/send-email-thru-gmail-and-others-in-wix-code