No, it is not. I am sitting in the next city over. Both are still separate entities from Atlanta, and will stay that way.
I now they are separate municipal entities, but one can get on Barrett Pkwy, and unless you happened to see the signs, never know at which point you left Kennesaw and entered Marietta, that also is a separate entity but is still pretty much Atlanta. Or Duluth. Or Roswell. Or any one of the dozens of other small towns spread across Fulton, Gwinnet, and DeKalb counties that make up “Atlanta”.