I guess from having a closer look at the cat-elog page, that they are?
You would have to ask a hard question
Linnaeus, 1758 described
H. plecostomus from "India." It was later "fixed" to Surinam, but if you (like me) think Linnaeus meant "Indies," his type could have been from any one of several Caribbean localities. Suriname was fixed by Boeseman who was doing a lot of work with loricariids in Surinam in the late 1960s. I can not say however if fixing the holotype was a brilliant link to Linnaeus' work of 210 years earlier or not. It strikes me as very coincidental that a Dutch scientist working in a Dutch colony just happened to connect his catch to Linnaeus' original description. An amazing connection since he did not have much, if any, material from other Caribbean locations to compare to Linnaeus' original description. I have never looked at Linnaeus' original description, but my guess is that it could be just as easily "fixed" to a half dozen valid spp. as it could to Boeseman's fish.
So
H. pleco either ranges throughout the Essequibo, Orinoco, and coastal Venezuelan systems (i.e. the Tuy drainage and others) or it is an Essequibo drainage fish and the
Hypostomus found all over the Orinoco is an undescribed fish, as might be the Venezuelan coastal population(s).
The only specimens I am aware of in the hobby currently come in from collectors near Villavicencio, Colombia (and these are what we are calling
H. pleco in the Cat-elog). These are not common shipments however as it is hard to undercut the "common pleco" breeders in Florida and the Far East on prices and very few hobbyists appreciate the difference.
The Orinoco population has a huge range, but is far more numerous in the north and west in white water rivers that are closer to the Andes and have a bit more current. Further out in the llanos, as the ground flattens, they become less common, and by the Orinoco itself, are uncommon by comparison. These lower and slower reaches of the rivers are where we start finding the woodeater
H. cochliodon as well as
Panaque nigrolineatus. I always assumed this was because wood in these areas has longer to soak and develop a thick biofilm without being washed away every time it rains. Areas where the two spp overlap is much more of a broad transitional zone than a clear demarcation. I expect it expands, contracts, moves up river or down, etc depending on season, weather and available foods. These ebbs and flows, over a very long time, probably allowed
H. pleco to colonize the huge number of Orinoco feeder systems where it can now be found.
Similar zones occur, for example between
Corydoras venezuelanus and
C. concolor as well as
Apistogramma spp but I never understood them as well.
-Shane