I grow lots of blueberries. I have found them to be fairly drought tolerant. I'm not keen on blueberries on high hugel mounds, maybe at the base of the hugel mound. Instead, do intensive, quality, blueberry specific
compost and mulching. Also concentrate efforts on proper soil PH. We all know how blueberries love acidic soil. The low trench hugel idea is right on... filled with slow release organic material like wood, bone, seashell, eggshell , etc. paired with an understory of nutrient accumulators and mycorrhizal fungi. Good Luck!