Ken,
Not sure if you realize it, but the LE's already detect the presence of a DMX signal. I don't have mine in front of me, but when in test mode, one of the channel LED's will light up if it is receiving a DMX signal. There's a couple of other diagnostic indicators in test mode.
Having an indicator while the board is in normal mode might be helpful... Don't know if there's any signals to drive more status LED's available in the current design, or if this would require additional circuitry.