I have the speedhut gauges and I had them add a check engine light and LEDs for blinkers, the brake light, high beams ect.
In the case of these gauges the power is supplied by a single wire to the guage, then to turn the indicator lights on, they pull to ground (as you have stated), so it's super easy to wire them up. Makes it real easy to wire them since you don't have to provide power and ground to every light.