For driving the dash LED, there's a resister inside the controller, so it can directly drive a single green or red LED. But, that only blinks a code when it turns on/off, or goes steady at full speed.
It should also work to tap directly into the speed signal. A couple things though: there is always a PWM present (25%+ when the fan is moving), and whenever the fan has power there may be 12+V present (some fans do, some don't). If you monitored the speed signal for your fan on and high speed LEDs, that might work pretty well.
If you ever find yourself in a fair fight, your tactics suck.
