So, you mean a buggy that doesn't have the required reflective sign, and in conditions that would make encountering even a car be a risky thing? And kerosene lamps only? No, and I have seen and passed quite a few Amish buggies.
I'm not sure if they all have the reflective sign. Laws vary from location to location. The faintly glimmering kerosene lamps don't make them very visible at all.
I suppose that it would be possible to speculate about all sorts of different scenarios that are rarely encountered.
I'm not sure how widespread the white-topped buggies are, but it would depend where you live. I've encountered several of them. Some white-toppers have LED lights and are easy to see at a distance. Some of them still use kerosene lamps. I'm surprised it's legal but you get them on roads with a 55mph speed limit.
They do, however, use the shoulder or part of it whenever possible, which I've never seen a slow-moving automobile do for the sake of helping the drivers of other cars. And, by the way, does your comment suppose that we should pass other vehicles WITHOUT moving completely into the other lane??
That varies from area to area. Sometimes they pull over to let traffic pass. Sometimes just for extra excitement a buggy will pull to the side but then suddenly swing back into traffic without any warning at all.
Depending on what the vehicle is and what road and traffic conditions are, I've never had a problem with things passing me without pulling entirely to the other lane. I don't cycle much these days but do walk and run a load, and where I live most roads don't have anywhere for a pedestrian to be other than at the edge of the road. If there's traffic coming both ways and nowhere I can go to get out of the way, somehow the cars have to get past.
That would be illegal in most states (and impossible on most roads).
Hence my comment about reasonably wide lanes, which would make it possible. Legal or otherwise, when I cycled everywhere I expected cars to pass sooner or later and was more concerned about them passing safely than adhering to some largely arbitrary number laid down in law. I'd rather someone slowed down to pass and gave me 2 feet of space, then flew past with a 40-50mph speed difference but sticking precisely to a 3-foot passing distance.
So are buggies, but they also are required to have extra warning devices installed.
Except the faintly glimmering kerosene lamps are legal, at least in some areas.
Most of the serious cyclists that I've encountered do take care to be seen--usually by wearing reflective clothing and/or having blinking lights operating. I appreciate and respect that when I encounter it but, if it's during daylight hours (which is usually the case), they are still less easily noticed than Amish buggies.
It's usually not hard to spot the more serious cyclists. They take care to be visible with lights and/or reflective clothing as appropriate, ride in a visible position and ride in a predictable manner. Few things focus the mind on staying visible quite like knowing you're the squishy bag of bones that isn't going to fare well if you hit, or are hit by, anything else on the road.
Maybe it's because of thousands of miles of cycling myself that I don't have a problem spotting them.