Plecos in my pond
I did have two plecos in my pond for two years, among with 5 kois, 6 gold fishes, and 4 other types bottom-feeders. The difference is that time I lived in Florida. I bought all of them when they were babies and our pond had algae. After two year they grow so big. And then we moved to North Georgia. Of course water temperature is colder, my heaters didn't survived the move (shows power on but no heat), and I didn't know it. As an emergency I had to put my common plecos in 36 gallon aquarium, where I have convict cichlids. Hours later one plecos was dead. The second one doing just fine, keep growing.
Just yesterday I bought two plecos for my new 20 gallon aquarium (water was cycled). I already have there four skirt tetras, two cat fish (babies), four tigers barbs. All of them small. I decided to get plecos. Only one survived again. All other fishes are fine. And the second pleco is doing great. Could it be they don't like to be two of them in smaller aquariums (my two big ones were ion 200 gallon pond)?
Back to the pond plecos - yes, with a heater and an all-year-warm region you can have plecos in a pond. When we had cold nights I could see them near heaters (I had two), while kois and gold fish were enjoying cold water.