First off, that's only .88 mame. I am working on updating it. With my old computer crashing I lost some programs I made to make updating the site easier. I have to remake those. With this new job and moving I just haven't had the time.
Anyway, about 95% of the cocktail games are vertical. The two that I can name off hand that are horizontal are warlords and space duel. Though warlord's cocktail mode was more of a 4 player vs 2 player switch.
As you see the list isn't that large, if you had some time get a hold of the listxml output (mame -listxml > output.xml) and search for the "<dipvalue name="Cocktail"/>" values. Then look if the game is horizontal or not. There should be an orientation tage for each game too.