Everything I read indicates the ghillie suit was an invention of Scottish gamekeepers

Everything I read indicates the ghillie suit was an invention of Scottish gamekeepers. I think it far more likely that the origin was the poachers the gamekeepers were after. The criminal element has always been more proactive than the enforcers who are mostly reactive. Poaching has been around since mankind first started possessing things.

For many, many years poaching was of no consequence to anyone except the landowners whose animals were being poached. Today poaching is a global concern as we see more and more animals becoming extinct due partly to poaching. Here in the USA it is not the problem that it is in Africa and other countries that have animals wanted on the global markets, for things like elephant tusks, rhino horns, bird feathers, and tiger piss.

I don't find any indication that the ghillie suit plays a role in these large scale poaches, but they are used by poachers and wardens alike in the more mundane efforts at illegal gaming. It's a wonder that more poachers and wardens aren't shot by mistake (or on purpose) while wearing their camouflage. I can just imagine a poacher opening up on a "deer" and the "deer" returning fire.

Poachers are not the only criminal element that spawns the use of ghillie suits. Drug dealers, Smugglers, and almost anyone doing anything where concealment comes into play, will sooner or later try a ghillie suit. The same can be said for their counterparts in law enforcement.
On a brighter note, the vast majority of ghillie suits are used in legitimate endeavors. Legitimate hunters and paintballers account for most. A number of them are sold to wildlife photographers, birders, and other nature observers. A few are bought by party goers, trick-or-treaters at Halloween, pranksters, wedding guests, and who knows what next? http://www.outdoorjacketsale.com