Hi
I have only just seen this post so I will add my own opinion.
I have fished Los Roques on 12 or 13 different occasions. I have caught lots of different fish, from tarpon of up to 100lbs and bonefish up to 11-12lbs.
It is a very unique place because of the amount of bait fish that are found at many of the beaches.
I have fished for bonefish with many different flies.
When I first went there some 10 years ago there was not as much fishing pressure as there is now and the bones would take anything.
4 or 5 years later they would only take very good bait fish patterns - hence the gummy minnow. I experimented with different patterns and together with Jan Kristensen (of Tapam fame) I came up with a floating gummy minnow. We fished them on a couple of trips and were amazed at the way that the bones would come up to the surface and take the fly, like a dry. On my last few trips I have hardly fished another fly. It is extremely exciting, almost horny, watching a fish with a mouth shaped for taking things from the bottom trying to eat a floating fly. - They quite often miss.
Regarding the debate of is a gummy a fly or not, I think is is a little pointless. There are now flies that fish just as well as a sinking gummy minnow but made from "normal" synthetics. Look at the Los Roques Minnows from Sportfish :
Los Roques Minnow Green .
The floating gummy minnows that I use do not catch as many fish as the other flies but they catch larger fish and it is extremely exciting fishing.
Have fun
Pete