Wouldn't a good flatbed scanner be better for this purpose, presuming that the originals are not framed?
The problem with scanning is time. I'm going to have 3 days to copy hundreds of photographs, and each photograph has a caption on the back which is needed as well. At 2 minutes per scan per side we'd get back logged by noon. I'll have 2 or 3 researchers pulling prints (at the National Archives, NARA) faster than I could scan them.
NARA does allow scanning though.
I did a comparison of a WWII B&W print with excellent tones that I scanned with a flatbed (a much better Epson than probably could bring to DC) vs. a copy shot with a Nikon D1x (RAW capture) and a Canon 1DsMkII. All printed at their default 300 ppi size, and then all printed at 22" wide (the width of the book we're producing) after interpolating them up w/Bicubic Smoother. The 1DsMkII was certainly sharper than the Nikon (17mp vs. 5 mp) and the flatbed was almost as good... For THIS particular workflow, the camera won out.
Also, I'm not sure if flatbeds can scan RAW, and the 12bit capture might give an additional tonal edge.