FWIW, there are only two games in mame that use the "vertical" spinner (IPT_DIAL_V, as mame calls spinners "dial" or "dial_v"), and only one of these games has both dial and dial_v: dragrace & offtwall, respectively. However, offtwall has the dial and dial_v on different players, and I don't why either of the games aren't just using the normal dial input.
This doesn't mean there are no arcades that etch-a-sketched. Not only are not all games in mame yet, but if an etch-a-sketch game was in mame, the controls could have been mis-documented as either a trackball or as player 1 and player 2 dials.
Still, I find it hard to think of a game theme that would have two spinners per player, except for an etch-a-sketch game. I too would be interested in seeing the CP if there was one.