I won't touch the first question with a 10-foot pole, because depending on which side of the fence you are on, you can find heaps of literature that supports your position and disses the other. Chiropractic definitely helps some, and hasn't helped others. Same as any medically-related field, only the numbers may look different.
As for being traditional medical doctors, I'd have to say yes and no. In some states, chiros can't call themselves physicians (state law), while others, they can. The training is different, and the scope of practice different, from MDs and DOs. One might compare it to a specialty doctor, only the basic curriculum in training often looks different from other schools. (I know many MD/DO specialists will vehemently disagree with this, specifically because of the differences between chiro and med school; these folks might make the analogy between chiros and PAs or NPs in a specialized field.) While MD/DO have to delineate their practice with board certification (Family Practice, cardiology, internal med), chiros do not. Some stick with mostly manipulation; others delve into immunology and nutrition. This is hotly debated in circles which love controversy.
Medicine has done a heck of a lot of evolution over the ages. Chiro is relatively new, but modern MD med doesn't look a whole lot like med did 150 years ago, either. Both fields continue to change with research and experience. Perhaps the main differences aren't always in what is done for the patient, but what the underlying beliefs are: the health of the musculoskeletal system how that directly influences nerve relationships is often how chiros describe their philosophy, with the caveat that they treat the whole patient. Allopaths do not wholly disagree with this in principle, but are trained and equipped to look at reasons beyond this for illness and disease. Their scope of treatment is much larger, including prescription drugs and surgery.
I'm sure there are many others out there who'd love to comment...?
