There seem to be many factors involved in coral spawning, and spawning activity won't necessarily result in disaster. Sometimes stress can trigger it. In some established, mature tanks mass spawning events can be a regular annual thing. I don't know of a study that's been done to test just how much of a factor artificial moonlighting is in regards to captive coral spawning activity, but I know many people think it's a factor.
I've never experimented with the whole thing myself, but there are lots of people who use moonlights and have never had a spawning event. Then again, there are people who have regular annual spawning events with no moonlighting. Personally, if I was interested in the aesthetic value of adding some moonlighting for nightviewing, etc., I wouldn't hesitate to add them.
