An interesting theory. I'm not sure I can buy it. From my reading, there were millennia between Ismael and Muhammad. 
"He will be a wild donkey of a man;They claim, well, it's true that this describes the Arabs so they must have descended from Ishmael. That, of course, is the fallacy of the undistributed middle: A is B and C is B so A must be C (or C must be derived from A), "Descendents of Ishmael will be troublesome and hostile, Arabs are troublesome and hostile; therefore descendents of Ishmael are Arabs." This is as true as saying, "Dogs are mammals. Cats are mammals. Therefore, dogs are cats."
his hand will be against everyone
and everyone's hand against him,
and he will live in hostility
toward [b] all his brothers."