TEP,
The photo of those bunkers at Deal in NJ are man made, without a doubt. There is an old photo that I've seen of the sand pit at Garden City where there are also tongues of grass intruding right up the face of the ridge. They could be natural or man made, but my guess is they are that way because maintenance wasn't so anal.
I don't think the idea of putting grass in the bunker, like the ones in NJ, was a wholly original idea. I think an early practitioner of course building saw that same type of situation on a links course, constructed it somewhere, and the element was added to the architect's palette, to be used sparingly.
edit: page 8 of the pdf.