It depends. It all depends on the cause of your lower back pain. See your to determine the cause. A do is a type of medical dr who has been trained in treating muscle/skeletal problems & may be able to help. Do's can use different techniques--osteopathic manipulative medicine to help treat low back pain-kind of like a chiropractor but also using gentle techniques like stretching, relaxing muscles, realignment.
It can. Both chiropractic care and osteopathic manipulation have been shown to be effective for treating low back pain. The advantages of seeing a do is that, being a doctor, they can offer a more global treatment, using manipulation, medicine or whatever you need to get better.
Spine Specialist... Certainly an orthopaedic specialist can diagnose, however in my view a diagnosis and treatment utilizing the least invasive protocols possible is a preferable solution. There are many good ortho doctors who will refer out if surgery is not optimally indicated, however there are also those who will operate because "they can". Whichever route you choose, select minimally invasive wherever possible.
Limited. This is their stock in trade but they do not offer actual diagnosis (everything is due to 'subluxations') and you will receive a deep massage which cannot cure anything and might miss something serious. For lower back pain always see your orthopedic specialist first and follow their recommendations.