Cutting anything cementitious is probably not a great idea because the fine dust may muck up the saw despite the dust collection. Now if it's just a few cuts and you really want to, the only thing you will do is potentially dull your blade, but keep in mind that should the saw need repair during its warranty period Festool may not be thrilled about your using it to cut cementitious material.
In Europe I believe cutting cement board with a TS is approved, not sure why it's different in US.