yes, but i doubt they made that rule with USB powered hubs in mind. They'll probably always assume you are direct connecting to be on the safe side.
What's supported and what actually works is often different. Dish's published requirements are definitely on the conservative side - and I can't blame them for it. Non-powered hubs almost always seem to work. Non-powered drives not as much.
There has been a lot of discussion on externally powered vs usb powered drive and the only real answer is it depends. With a powered hub, it seems to usually work, but I think some of the notebook type drives seem to power down too deeply and don't want to wake up.
USB powered drives connected directly to the receiver have been a lot more hit or miss. Seems to depend a lot on the drive's power requirements and even which revision of the receiver it's connected to. Some drives are recognized, but don't seem to get enough power to actually spin up and do anything.
Personally I would prefer putting the load on the hub's power supply than the receiver's.
Of course all this experience in the forums has been for 622/722/722k. Hopper may have better (or worse) results in general.
Bottom line, if you're purchasing a drive and can't return it, get a powered one to be safe. If you have a drive to experiment with, then try it out, but remember you won't get much help if it doesn't work.