There's more than one flavor/brand of "bearing buddies". King marine installs a type of bearing saver that looks like bearing buddies but work completely different. They do indeed get grease to the back bearing. It is my understanding that actual bearing buddies do not.
EDIT:
found this on king's website.
"SUPER LUBE" WHEEL BEARING LUBRICATION SYSTEM
Super Lube is a non-pressurized, flow-through system that lubricates both bearings in the hub. A flow-through system means that fresh grease enters through the inner bearing and out through the outer bearing removing moisture and contaminants every time grease is added."