Pat:
No idea. That photo is from very early on, so my best guess is that the bunker was original to the course. Whether it was part of the original design or if it was a design modification during construction, I don't know. And it is possible that it was an addition made after the course opened and prior to the taking of the photo.
Here's a summary of the early changes to the hole:
1934 - 150 yards - The tee was positioned beneath a frame of three pines, which soon died. The wide, flat green was built by cutting earth from the far bank of Rae's Creek and depositing it on a ledge. The original bunkering consisted of a long, skinny one in front and a tiny one atop a hill behind.
1939 - 155 yards - Roberts directed Maxwell to enlarge the green on the right by digging out dirt from the bank behind the green with the possibility of exposing rock. Roberts wrote "I think it will add to the thrill of the hole, as a very strong shot will strike the rock and bounce most anywhere." A month later he wrote Maxwell to say "We do not wish to expose any rocks on the bank." Maxwell turned the pits into bunkers.
1951 - 155 yards - For years the area between the tee and the creek as an oft flooded bog (in 1936 rowboats were considered to get players to the green). When Rae's Creek was dammed for flood control in 1950, a tiny stream off the tee was buried in pipe, and the entire area was raised a bit. A swale was created behind the green to remove water, and the bunkers were relocated.
As for the Olmsted plan, I'm going to quote some moron on its reliability as a source: "While the Olmsted schematic is a nice rendering, it should not be regarded as definitive."
I would note that since the bunker was at the top of an incline, in actual distance as viewed from overhead it was probably closer to the green than it appears in the photo.
By the way, any thoughts on Bubba's shot into 15 on Sunday (which was from left of the three trees the designers located in the 15th fairway as they appear in the Olmsted plan)?
Sven