No. With the obvious caveat that if you have both available, go with the higher-wattage iPad charger. In a pinch there's no harm in using the iPhone cube.
it says not charging, but it's charging slowly. you get the same message if you're charging via usb. i rarely use the wall charger unless i need an immediate boost in a short time. i find that when plugged into my computer, the ipad will charge from 20% to full overnight without issue.