No, it is not possible to import CAD files in FLUKA geometries.
You can try to use FLUDAG, but beware that it is neither distributed nor maintained by the FLUKA.CERN collaboration. Nevertheless, several questions have been asked and answered on this forum about (here there is an example), you can search for these with the SEARCH function of the forum.
FLUKA is able to simulate the incoherent interaction of X-rays with objects, nevertheless it is not able to simulate the coherent interactions that generate a diffraction figure, i.e. it is not good for crystallography studies.