HUM is independent of using HU. When you say the storage location is HU managed what you are basically saying is that all the stock needs to be contained in HUs and the sum of the HU stock is equal to the MM stock.
If your storage location is HUM then you need to use HU, if it isn't HUM then you can use HU but don't need to.
If you want to disable the generation of HU automatically that is controlled in the delivery item category.