You cant fly a quadcopter if all the motors are spinning in the same direction (as you need the counter rotating motors to compensate for the torque/yaw effect)
However it is technically possible to use all CCW motors and have two of them spin CW, as brushless motors can actualy spin any direction. When we refer to CCW/CW motors its actually referring to the thread on the nut as the thread is designed so that the nut tightens when the motors spin. So if you are using all CCW thread on your motor and you make sure the nuts are properly fastened then its totaly fine to use.
Hope that helps