Can you actually feel the chip? I've had my iliac crest pretty much removed on both sides for the grafts to my 6 neck fusion anterior. I recently had the posterior fused from C3 thru T2 with rods and removed all the spinous process. I remember the first surgery when they used a graft from the iliac crest and the pain for about a month after surgery was BAD. After that they didn't hurt as bad if at all. If there is a chip from maybe a motocross injury that may be related or can't remember the incident, could be there. May be a x-ray can tell if there is a chip. I'm no Dr. but don't see a relation in the chip and the sacral area, but don't mean something isn't going on, after all he has a injury prone hobby. From all my experience with ten total spine surgeries neck and back, hands on anything always helped me, as long as it isn't damaging the patient and don't think it is.
I personally would not take any chances. I used to see a Massage Therapist for my neck back and shoulder problems and have stopped. My Dr. told me too. Just to ease your mind and precautions tell him he needs to follow up with his Dr. and get a release before you treat him anymore. Massage feels good, but if theres something underlying you may be doing more harm than good. Has he been to the Drs. do you know?