A cam is a good idea.
Nope they also eat foliage & a picture would show that only easy accessed parts are bothered.
I have heard ( no pun) that ultrasound may work.
I need get more info on this .
Carolyn is correct. The Hoary bat is strictly an insectivore. It is something else that is stripping the leaves and eating fruits. You definitely need to document this with hard evidence. Who knows, you might have just discovered an up-to-now unknown frugivorous species of bats in Hawaii. For your sake, I really hope that there are no frugivorous bats in Hawaii.
Nobody yet knows what the Hoary bat hearing range is. Although you can get a decent estimation of what the animal hears based on its echolocation frequencies (which is available), the use of an ultrasonic repellant is not a good idea, since pollinating insects and other good bugs may also hear ultrasound and stay away from your blooms. Ultrasonic repellant has never been an effective deterrent, simply because high-frequency sounds are very directional, easily blocked by obstacles, and does not propagate far.
So your best bet is to first prove that the Hoary bat is raiding your fruits, and is indeed a frugivore or omnivorous in its food preference. There are such bats, but not in Hawaii, unless they were "accidentally" introduced to the islands. It would certainly be BIG news to the scientific community.