The USB host is here, yes, but it's absolutly not powered up. The USB host of the TG01 is powered up.
So indeed, with an external power source, it may work, but I think nobody has tested the HIDgamep.dll (the one that allows the TG01 to handle usb gamepads, the one I was using on the tg01 for the dicota gamepad or other gamepads). the registry part that has to be modified to link to these drivers is the same on the HD2 and the TG01, that's already a good indication.
I've tried to power everything up using an USB host, but it's vain. The only solution is the one you see in the videos you've linked to your message: cutting an USB cable (or powering the dicota itself?) but I haven't tried so far.
Just note one important thing: on the TG01, using an USB gamepad was killing the battery very quickly, and the USB host function was stopping when the battery was under 30%
You could play muuuuch more time using the MSI BGP100 bluetooth gamepad.
So my dream would be to directly put a battery into the dicota, not to have a modified cable with an external battery at one end and the HD2 at the other. Such a system wouldn't kill the battery of the phone, what would be better than on the TG01.
I fear I'm not a good enough moder to do this myself