If the minds are being simulated they could be manipulated to ignore any evidence they are in a simulation.
Yes, this is exactly my problem with claims about the 'real' universe if we are, in fact, in a simulation. It might be literally, programmatically, impossible for us to infer anything about it. The analogy I like to use is Pac-Man believing that the entire universe exists within the confines of a blue-walled maze.