I always was under this impression, mostly due to stuff being in one shot and not another-Figured if it was meant to be there it would be in all the shots showing that area.
What about Bigfoot, Easter Eggs and The Chambers signs? They are obviously meant to be there, but none appear in all the shots. These are things that WGT has inserted intentionally.
As it comes to the "normal" stuff, like ball markers, random "phantom balls," etc, we can make many presumptions but, IMO, we will never really know if such items are simply failures by WGT to remove, left intentionally, or put there by WGT.
We can presume from WGT's response, as to the two people behind the Pebble Beach green, they were not put there by WGT, intentionally, but just happened to get caught in the mapping process.
Whatever the reasons, I, for one, thinks it cool, and provides for another way to enjoy what WGT has to offer.
As for, what I call, the "phantom balls", they definitely were not on the course when WGT did their magic. These balls are the same as what we hit in the game. Many times, if I am teeing second, I can see what looks to be my ball in the fairway, while my playing partner is hitting. In the beginning, it seemed that, when I did hit, my ball landed where I had seen the "phantom" ball (before I hit). Eventually, I realized that it was just coincidence if my ball landed there as, just as often as not, my ball would land somewhere else.
I think seeing these "phantom" balls before hitting may have led to the conspiracy theory that your play is predetermined by WGT. (Or is it?)