MCT is mostly capric and caprylic acids. These fatty acids make soap that's even more stripping to the skin than the lauric acid in regular coconut oil.
MCT will saponify just fine. I personally would not ever use it for soap making, however. Some people do use it in place of or in addition to regular coconut oil. I suspect they have have the idea that the properties of the MCT will carry over into the soap made from MCT.