Yes, definitely a hack. Turns out it works well for me since I'd rather have my reminders in the app where I keep track of my tasks and not in a separate Reminders app. But, definitely not a true integration. I can't add tasks without a due date/time and certainly can't indicate other attributes of the task such as priority, tags, etc.

RememberTheMilk already has connected Siri to their task management app by basically redirecting the connection to the iPhone's reminder app. They talk about it on their blog, here: http://blog.rememberthemilk.com/2011/10/we-taught-siri-to-add-tasks-to-remember-the-milk/.