Are there any Fide Masters, who also happen to be scratch golfers?
That would certainly help putting this one to bed, as they could explain the relative difficulty of both levels of achievement.
Three sources have been given:
source 1
source 2
source 3
The statistics of the first two sources seem to be in some degree of agreement, those of the third (which provide statistics in terms of actual 18 hole scores rather than handicaps) seem to provide a very different picture.
It could be that the first two are accurate and the third one inaccurate.
It could also be that the third one states an actual picture rather than a theoretical picture, or it could be that there is a sort of "blaggers, sandbaggers and braggers" effect first intimated by Paul Cooksey above, but I would have thought that some sort of ethics process would minimise that sort of thing in such a commercialised activity. One might point out that the sources are all American, and if one were to extrapolate from dubious processes used in maintaining the USCF ratings list, one might envisage all sorts of nonsense.
I suspect, however, that the fact that I don't understand the golf handicapping process correctly, is the real reason that these statistics appear to disagree.
Using source 1, scratch is approx. 210, using source 2, scratch = 202-204, using source 3, scratch is approx. 196-198.
Bob Clark, both a graded chess player and a handicapped golfer, initially proposed that scratch would equate to 180, but then admitted that that might have been a slight underestimation. This would tend to suggest to me that scratch lies towards the lower end of that range from 196 to 210.