What does a karateka need to know about the Japanese sword? Well, nothing really.
Karate's roots are not in feudal Japan, where the katana was ubiquitous. Yes, there were plenty of swords in old Okinawa, but as an art directed mostly at unarmed combat, karate emphasizes movements and strategies that are, in many ways, incompatible with those used to make the sword an effective weapon.
It's odd and sometimes unnerving to watch karate demonstrations given by sword "experts." Assuming that a person can use a sword just because he or she has experience in karate is like assuming that because your basketball skills are excellent, you'll be a good lacrosse player — they're both sports that use a ball, after all.