Seeing an American Black Bear in Zion National Park is rare but not unheard of. Since bear sightings are so rare each one, even a possible siting, should be reported to park officials. It is important to know the procedure for bear encounters on the off chance that you may see one.
In general, no need. I camp in bear country all the time with no gun. Preventive measures of not leaving food out for them to smell will go much further to be safe than a gun Bear spray is also much more effective than a gun.