It's hard to say. I know a judge just issued an injunction to allow the cheerleaders to keep doing it, but it's likely to go higher. The problem I see is that it is a school-sponsored event on school time. If these were aetheist cheerleaders with big banners citing "No God," how would it be handled?
I like the idea behind what they're trying to do, but then again, if you have others that attend the school under a different religion, should Christianity be forced on them when they're involved in school-sponsored events?
It's a slippery slope now days.