@Riley: No worries. I have confidence that you know why you've done as you have, it has been very elegant and simple so far, which is saying a lot in this paranoid era. But I'm not entirely sure your estimate of time would be true, assuming you had 10,000-100,000 campaigns generated at a given moment (this is not that optimistic considering the fervor around the site right now) and the griefer merely wanted any one game, not a particular one... It would be like Roulette until your anti-brute force algo' blocked them, but yes, it would certainly take some time and dedication, and could be worked around. The Internet is full of griefers and spammers... I unfortunately assume they're getting ready to ruin my day at any time.
My concern is closer to what David raised above... if I give a link out to someone, and say... their annoying kid brother gets his hands on it, there is currently no mechanism for keeping the environment locked down to set players. Suddenly you're in the middle of the game, and a new video feed pops up with an anonymous filler image and a Rick Roll. Even if you change the link, it then gets forwarded on, and again purloined by the idiot kid brother... rinse and repeat. I'm not saying your current system is without thought, or isn't in its own way ingenious, but... I err on the side of caution with such things, personally. Seemed prudent to suggest at least one level of control for the DM beyond passing out a link, considering the potential for abuse. I have a lot of faith in the DMs I've known, but being secretive and properly securing their 'passwords' isn't something I attribute to all of them. Seems like a problem that could bite later on, and make its way to the suggestions again.
Not an immediate need; never thought it was. But this is just a suggestion, even if a longterm one. :)