It's really hard to find good pictures that let you see the tuners. Tho koa F-50 shown on the NAMM video has custom, open-back tuners that do not have the slots. Other guitars appear not to have the slots but it's hard to tell because the resolution of the video isn't very high (you can't really see them clearly on the 12's either, but I think they're there).
I looked at another picture of the F-512 headstock (from the 2010 NAMM catalog) under a magnifier and, definitely, the string end is stuck into a hole in the end of the tuning post shaft, bent down so that it lays in the slot, and wound around the post as the string is tuned up -- just like on the bass posted in this thread. The catalog doesn't have headstock enlargements for any other models, so I couldn't make a comparison. The smaller pictures of 6-string Traditional models don't appear to have the slots, but this is by no means definitive.
So, based on what little I can garner from available images, I'd say the slotted tuners appear to be exclusive to the 12-strings, although, again, this is not a definitive determination. If folks check out New Hartford Guilds in person, this might be something for them to look for.