Grinding melted latex off a pizza stone?
It won't suffer much from having a millimeter or two of material removed in one area, so I'd just go ahead with the Dremel and grind it down to clean stone rather than resorting to chemicals that may or may not work and may or may not impregnate the stone.  There's no substance made short of diamonds that can resist a grinding wheel.  Worst case is you end up with one side that's unusable for anything that requires a smooth surface, but otherwise it should be fine.  It's mainly just a rock, after all.