Not really a chance on earth.
Despite knives being hiders a lot, they can’t help their big size and urge of coming out in the open at some point to stretch themselves.
The only two ways fish can survive with piranhas is if they are small and fast, or hide constantly and not move much. Knives don’t really fit into either category.
Arguably they do hide, and they can hold their ground. But they certainly are not small, not fast and constant moving, and have no 'body armour'.
They would be low down in my 'recommended worth risking list'.