Games with values of dt above 0.1 tend to become unstable. Everything is stepping so far often collisions are missed and the player can effectively teleport around.
So how does it help prevent cheating to allow this? It seems like it will make cheating worse. Set your FPS to 1 while running towards a wall and you can teleport through it. However with the current design, you would probably still bump in to it.
A better way to handle this would be to require a minimum FPS of 15 or something, and don't allow scores to be registered for them. Or keep separate scoreboards for slow devices and fast devices based on average FPS - you don't want to annoy or blame users who just legitimately have very slow systems.