The doc that did my Basic Med has been doing DOT physicals for truckers for years. When Basic Med came along he tacked it on, as the exam is very similar. Generally speaking, and based on what others have told me about their Basic Meds, I think it's largely the same pool of doctors doing Basic Med, DOT, sports physicals, employer physicals, etc.
When I was racing cars, I heard all the same questions and fears about our required physicals, but when it came down to it, many walk-in clinics were perfectly fine with doing them. Much ado about nothing. The exam for racing drivers was slightly more thorough, as it included an EKG and a stress test, and the physical demands for driving a car in competition are MUCH more strenuous than those for flying a plane.