I doubt a pleco could “eat” a fish like an Oscar can but I remember a thread here I think it was where a common pleco learned to catch and eat goldfish because it was the only source of food he was given. I have had a 9” rhino pleco with a 4” African knifefish and he didn’t mess with him. I suppose it depends on if you’re incredibly unlucky, if it’s a meat eating pleco, if it’s aggressive or not, but generally I’d say it would not. Do take my words with a grain of salt though since every situation is different.