In renting a hotel room, I assume it includes utilities such as electricity, water, etc. It is the hotel's responsibility to deal with suppliers, even if they don't have control. Of course, a hotel could have limited backup power available that would power the lobby, kitchen, wifi, etc.
I wouldn't expect a full refund for the one night, but I would expect some accommodation. For a 30 minute outage, no i wouldn't expect anything, but 6 hours is a long time. I think 33% off the bill or some points would be reasonable.