Another counter to the likely made-up explanation of hiding one's feet is that in some periods, the style for hakama length were very short - like halfway up the shin.
There's a similar thing I always thought was bogus. Some say that when holding the sword at waist level with the blade pointing down and back that you should angle it such that the opponent cannot see it. like this is going to be some big advantage. I mean aren't you supposed to be in a freakin' sword duel? If your opponent is so stupid as to not wonder why you are standing with some surprise tucked behind you, or, worse, to have forgotten that you were just holding him at bay with a sword pointed at him only seconds before, how much tactical advantage are you really going to need anyway?