So they should be able to tell if the asteroid has heavy metals, such as gold, yes?
I doubt it. I have forty years of radar engineering experience. This sounds like something that is a hybrid of inverse synthetic aperture radar (ISAR) and ground penetrating radar. ISAR can characterize the width (cross range dimension) of a rotating body as a function of range, and ground penetrating radar gives a profile of reflectivity vs. depth. Metal detectors are not ground penetrating radar, they detect magnetic field anomalies caused by eddy currents in metals.
Most small asteroids are solid chunks of rock, held together by the tensile strength of their material. Larger asteroids and comets are rubble piles only loosely held together by their weak gravity. A density profile might allow us to determine which model fits. This experiment is a trial run.
It is interesting and troubling that the world's largest radio telescope, FAST, located in China, is not involved. Is that because the U.S. does not trust China, or China does not trust the U.S.? ("Da feelin' is mootchal!") Or possibly there are legitimate technical reasons.