What bothers me about this is that there seems to be this idea that there are "school rules" that can conceivable cover ANY off-campus behavior, actions or activities.
There's an argument that certain off-campus behaviours should be covered by school rules; cheating (i.e. hiring someone to do a school project, etc), kids on a school team using performance enhancing drugs, possibly bullying. But there's not much, and certainly any kind of the speech, "decorum" or association school rules should never be enforceable outside of official school activity.
However, the idea that any private or public school administration has the authority to get the passwords for someones online service account and search the content is ludicrous, and for the organization to actually put that kind of thing into writing as standard procedure (if we think they're up to something, we'll coerce a student or parent into violating the terms of service of an online account) into writing is just begging for a lawsuit.