It doesn't matter if he existed or didn't exist at this point. What remains, still remains!
Same as it doesn't matter if Jesus existed or not, which there are also a lot of people who think that.
But nevertheless, you have a billion+ christians on teh planet.
The matter of his existence is completely aside from what is extant and attributed to him now. In both cases and more.
Hui ke DID exist and is documented. So if he was the actual founder of zen and ta mo was not, then so be it.
George Washington wouldn't be the first president of the USA if not for a general named Lafayette from France. But you don't hear too much about him outside of military circles really. Most americans have no idea about the role of the French in winning them their country and their independence from the British. George never cut down a cherry tree either and Christopher Columbus did not discover America.
there's a lot of wrong perceptions out there. But they don't take away from the truth, if anything, they serve as a launch point for discovering deeper truths about a subject if the person has the curiousity and open mind to look and to not be lazy in their thinking.