A CMM is can be used for the typical dimensions off a 2D drawing: diameters, lengths, forms(roundness/parallelism/flatness), position, etc. A 3D model is only needed if you are looking at 'complex' shapes such as the form of a mold, curves, turbine blades.
Some CMMs can even handle the 'standard' complex shapes like gear forms or threads off just a 2D drawing.