I haven't had a Pelvic Stress Fracture but I have suffered with pregnancy related pelvis issues for nearly 2 years after birth. I can't offer you any advice for your specific injury but I feel for you, pelvic issues are no fun as it can impact on so much else. I took to swimming (front crawl though) which has been an absolute saviour for me. Luckily now I seem to be able to run further again but I'm keeping up the swimming.
With the right pair of shoes for you the impact is supposed to help with bones and joints according to recent studies (unfortunately I have no references). Having said that off road is also good for your core stability. I enjoy both to be honest so like to mix it up.