some catts bloom on dried sheaths, others bloom from green sheaths. occasionally catts will put up a sheath and then fail to bloom from them--this happens most frequently on the first sheathed growth as presumably the plant overestimates its energy reserves. nothing to worry about.
sheaths generally do not need to be split open, unless: 1. you have a clone that is known to require some splitting for the buds to develop, which is uncommon. in any case you can tell that the buds are having trouble splitting the sheath on their own; or 2. you see a good quantity of moisture within the sheath, which may lead to rot of the developing buds. and it may help to split open the tip with a sterile instrument to let that moisture evaporate. if the sheath is dried, chances are there is no such moisture.