I probably just don't understand the addOpenFormFeedback method but I threw this java action into a microflow and am calling it on a button press. Nothing is return from the xas call. Is this method supposed to display that form on the page?
Yes, that method is basically the Java equivalent of the show page activity in a microflow. Your code is adding the feedback to the Mendix system context instead of a “normal” user context, which explains why you do not see the page anywhere.