Interesting advice. As far as loosening up goes, it is true that the body makes hormones to loosen the ligaments/joints so the darn baby can pass through. However, everybody is very different. And even as far as elasticity and return to original shape goes, there is variability. Age is a huge factor. The younger you are, the more likely you'll be the same after delivery as before pregnancy. Most women do not have a problem with joints returning to normal. It is very common for muscle and skin to remain permanently stretched.
So I doubt "permanent damage" to your pelvis but I am not a huge advocate of riding while pregnant. Whether we like to admit it or not, riding is an extremely dangerous sport. Rollers sound like a great idea.

