I’ve never heard of someone, Jewish or not, who argued that Christ never existed. If it really is a shroud of Jesus, it doesn’t really prove anything one way or another (unless you believe that the shroud was created supernaturally, I suppose)
I happen to think that -- from a purely physical standpoint -- the Shroud was created through a very "natural" process (i.e., the process that was used to create it could be replicated in a laboratory environment if the same conditions were present). Does that make any sense?