Not sure about MA, but in Ohio one needs
"4513.23 Rear view mirror.
(A) Every motor vehicle, motorcycle, and trackless trolley shall be equipped with a mirror so located as to reflect to the operator a view of the highway to the rear of such vehicle, motorcycle, or trackless trolley. Operators of vehicles, motorcycles, streetcars, and trackless trolleys shall have a clear and unobstructed view to the front and to both sides of their vehicles, motorcycles, streetcars, or trackless trolleys and shall have a clear view to the rear of their vehicles, motorcycles, streetcars, or trackless trolleys by mirror.
(B) Whoever violates this section is guilty of a minor misdemeanor.
Amended by 128th General AssemblyFile No.9, HB 1, §101.01, eff. 10/16/2009.
Effective Date: 01-01-2004"
http://codes.ohio.gov/orc/4513.23
At one point I thought I found something saying side mirrors were needed, but I am going to buy little mirror squares and put them up with the cameras. Unless I find some donut like mirrors to go around the lens.