Well it has been 30 days with the moon light on the tank so here is my update.
It does not seem to bother the axolotls. It does add to my enjoyment of my axolotls.
I work days and by the time I get home, take care of the dogs, fix dinner, and do all the things I need to do it is nearly bed time. The axolotls daytime light is an eight watt bulb from an eclipse 6 tank and it is on a timer. Comes on at 7:30 AM goes off at 8 PM. The moon light is on all the time. By the time I get to sit in my comfy chair and stare into my axolotl tank the daytime light goes off or has already gone off. With the moon light I can still sit for a while an watch them "be axolotls".
Last night they were very active; Echo was swimming laps back and forth for over an hour. Blingbling was hanging out on the tops of the plastic plants, moving from plant to plant every twenty min or so. Jude was digging holes in the sand. I have noticed that Jude digs a lot at night, holes in the sand down to the glass sometimes.