Well, I may or may not understand your question and my answer coincides, sort of, with another.

If you have an M&P Core, use the correct baseplate that comes with it from the factory. If you don't have a core and thus need to have the slide milled. Have it milled for the specific red dot you intend to use. In that case (a slide that needs to be milled for a specific red dot), no adapter will be or should be required.