Tricky, can the pendulum forehand (OHBH on other side, like Sampras) be hit with a straight arm?
Technically, yes. When you need to hit extreme CC shots on the run, lower your swing plane so that the finish is below the shoulder (i.e. "WW-style".) You'll end up with a reverse finish due to the torque, but your swing will be straight. It will look like you're slapping the ball wide.