There's not much consensus on chain maintenance. I've even heard that lubricants often do more harm than good since they attract dirt and grit. If I'm not mistaken some studies have shown that a clean unlubricated chain results in no loss of efficiency over a clean lubricated one.

Anyway, I doubt that using WD-40 is going to do much harm. I use a rust resistant chain on my winter bike and while it looks a lot better at the end of a season than a normal one it's still pretty much shot.