Ceramic pads work fine on cross drill slotted rotors. Metallic pads will work just as well, up to a point. Ceramic pads tend to last longer than metallic pads and score the rotors less. Under extreme braking conditions, a ceramic pad will dissipate heat and cool down faster than a metallic pad. However, the difference will not really be noticeable unless you are doing a serious amount of accelerating and braking. Street racers and high end sports cars are common users of ceramic brake pads. Slotted and drilled rotors cool down quickly and can provide better performance under extreme driving conditions.
For more info, see Pros and Cons of Cross Drilled and Slotted Rotors