Hey There,
I'm not a DBMA practitioner, but I have fought in their Gathering before. From my experience, they are completely open to someone coming in and training and fighting with them as long as their heart is in the right place. If you don't know what you're doing you can get seriously hurt doing what they do, so you should prepare yourself if you want to play. But from what I've seen, heard, and felt they are very open to new and different things.