They might, but probably would not gain much nutrient fom it as it is too hard for their stomachs to digest. Wild bears have been known to eat certain types of tree bark, horsetail and skunk cabbage, but not grass.
Black bears are not known to eat other species of bears, or to be cannibalistic in nature. Here is a detailed outline of their diet:
"Black bears are omnivores whose diet includes plants, meat, and...