In theory, the hügelkultur beds should store more water in the spongy wood base than a "normal" raised bed with just soil mix. In this drought year, I have seen a very big difference in performance and the hügelkultur beds are just doing a lot better. Having said that, you still need to water, or have rainfall, every once in a while to keep the beds hydrated.
I know a lot of people wonder if the galvanized metal panel raised beds would get too hot. Well, not as far as I can tell. My new galvanized metal panel hügelkultur beds are outperforming all my other beds, but it's not a fair comparison as I am able to turn on the water faucet for at least 30 minutes per day to water my galvanized beds in my backyard, whereas the beds in the main garden only get manual watering a couple times a week. But I don't think the soil in the metal panel beds is any hotter than the wooden raised beds.
My pepper plants in the main garden (with no running water) are only about 1 foot tall, and have maybe only 1 pepper on a plant. My pepper plants in the galvanized metal panel hügelkultur raised beds (with sprinkler running 30 minutes per day) are almost 3 feet tall and I have picked maybe a dozen or more of peppers off each plant. If the soil was too hot from the galvanized metal panels, then I would think the plants might suffer from the heat even if they are watered every day. I don't see any signs of heat stress in my plants in the metal panel raised beds.