In turbine work, a dowel pin which is located so it splits a joint line is called a radial dowel. It is common in turbine work (hydro and steam turbines), but not used as a key, just as a locator.Typically, these are used between turbine casing feet and sole plates, and on some shaft coupling flanges.
I heard things referred to as "dutchman" over the years by my old man and other mechanics. Typically, a "dutchman" was something to correct a foulup or unforseen bust in dimensions. My dad used to look at an extra heavy saddle under a door and tell me: "Looks like some guy wasn't much of a carpenter- hadda put in a dutchman". Around machine work and powerplant work, we took a dutchman to mean an extra heavy shim or spacer piece that wasn;t in the original design- something like a machined spacer to take up a gap between a pipe flange and the flange on a pump casing; a Blanchard-ground piece of plate steel drilled for the mounting bolts and stacked in on top of a sole plate with the thin shims on top....
The type of "round key" is occasionally used in places where it is impractical to take things apart to put in a key. My own experience was with a large side-crank stationary steam engine in a remote location. The crank hub was cast semi-steel and the crankshaft was steel. The shaft was 12" diameter and had been pressed into the crank hub with the hub heated. There was a key about 2 1/2" square. I was re-erecting the engine and saw there was a gap of better than 1/8" down one side of the key/keyway and the key had actually deformed a bit off its end. There had been relative movement between the crankshaft and the crank hub. Probable causes: Engine took a slug of water thru the cylinder while running, or, generator paralleled into the grid out of phase. The hub probably took a 1200 ton locomotive wheel press to put onto the shaft, even with some heat on the hub, so the kind of shock load to cause realtive movement and opening of the key/keyway fit had to be huge. The fit between the hub and shaft was still good, but I did not think it was wise to rely on the interference fit to transmit the torque from crank hub into the shaft. I was concerned tha tonce the fit had been broken by shock load, it's ability to hold things together was compromised. Either way, I had to secure the crank hub to the crankshaft against further relative movement. I opted to put in two round keys. To do this, I set up a big mag base drill (required a fixture plate and a few smaller tapped holes into the crank hub's "web"). I then drilled progressivley larger holes until I had drilled two holes a 1 7/64" diameter x 6" deep- half on the hub, half ont he crankshaft. These were then reamed and cleaned up with a brake cylinder hone. Two dowels were turned from some 4140 (or whatever truck tranny shafts happen to be). Final fit was made by polishing the dowels. We then had the artificial inseminator show up with his liquid nitrogen to chill the dowels, and we warmed the hub/shaft with a rosebud (oxyacetylene torch with heating tip). We heated the crank hub/shaft areas until they were warm to the point you could barely keep your hand ont hem. The dowels got chilled down in the liquid nitrogen, dunked in alcohol and then slid into their holes. We finished erecting the engine and I got the valves set based on the "new" dead centers since the crank hub had been moved relative to the shaft. The engine ran fine and pulled load, and I dumped it off line wiht full load as part of startup testing. That was years ago, went home and never heard anything further.
Would I recommend the round key in place of a square key ? For very light loads/small shafting, I would use a round key. For anything seeing cyclical loads or anything beyond very low fractional HP, If I COULD put in a square key, I would prefer to. Will the round key transmit the same torque as a square key of same width (diameter) ? In theory, yes. The shear area will be the same. Reality: The round key relies on a very good fit between the bore int he hub and the shaft to avoid a "rolling up" or wedging action. To avoid any chance of the round key rolling up or wedging, the fit between the hub bore & shaft has to be very close- a drive fit or light interference fit being optimal. For everyday use, where someone takes a pre-bored pulley or sprocket to fit on commercially sized shafting, the fit may be a little on the loose side as the pulley or sprocket hub may slide on with little or no force needed. This would allow some relative movement between the hub and shaft. Over time, under changing loads, the round key will start "working" or wedging/rolling. It is probably along the lines of the guys who wear a belt and suspenders, but if I had to use a round key on a pulley or sprocket with commercial shafting, I would lock int he key. To do this, I would drill/tap a hole half on the end of the round key, half on the hub or shaft. I would tap the hole as deep as I could, so I could use a long setscrew and a short locking setscrew. This would lock the round key against any rolling or "chucking".