This seems like a great idea to me, as it could get you a job, and make your service much faster, in that you could build your notification system into the class scheduling system, which would mean you wouldn't need to poll their system every 3-7 minutes - it could be event-driven instead. (Dropping a class could trigger a check of who's watching the class and notify recipients that way.)

Writing in that line or two of code would also take care of the school's strange DoS concerns.

Of course, if profit is the goal, this isn't an option (though it doesn't look like you're trying to monetize this... kudos for that).

Also, this removes the exclusivity from classhunt (as any student would see this while browsing the schedule online). I'm sure you can make more inferences about this option. (Less social capital in the business world as you have nothing to point at and say "I did that," etc.)