Actually, a wider chin is usually an advantage since the front view appearance tends to look more narrow with a genioplasty. See the surgeon and discuss your concern.
It would depend on what your goal was from a sliding genioplasty procedure. (final chin shape) A thick and wide chin bone does not preclude having a sliding genioplasty. Depending on the shape of the chin you seek from the front view it may change the type of sliding genioplasty done. (how the bone is cut)