I would be suspicious of any medical advise (including nutrition) that a Chiropracter tries to sell you. They are not qualified to do anything but what they were educated to do.
Some Chiropracters will offer a blood test, show you the image of your blood on screen and then point out the many things that are wrong with you. They will then proceed to sell you expensive supplements. These methods have been proven to be scientifically unsupported.
I remember hearing about the Blood Type diet several years ago, but didn't do much investigating. A woman I worked with at the time was on it and said she had lost weight, but the diet involved cleaning up her diet. I'm not sure it's eating for your blood type that works but the simple fact that you are eating limited and specific, clean foods.
For more information on what to expect from a Chiropracter and what to watch out for: http://www.quackwatch.org/