Incorporating hill training into bike and run training is not exclusive to cross-triathlon training, although it should be the core competence that all off road racers strive to achieve. Almost every cross triathlon race is going to require climbing up hills of various length and grade. The part of training that is crucial, and separates cross triathlon training from many road programs, is the focus on running downhill.
Being a great downhill runner not only allows you to stay strong in the closing miles of a hilly race, it also makes you much faster running down technical terrain. Fast feet and confidence in your descending skills can make an enormous difference on race day in an off-road event.