Actually they were around $22,400 according to the comment just under that. Still, I wouldn't be able to tell you whether or not they operated at a loss. You'd have to ask jedberg.
Let's say their CTR is 0.1%. That's 300k clicks/month. I'm building in some wiggle-room here, as a 0.1% CTR is abysmal, but often their ads aren't really ads. Even at $0.01/click, that's still $30k/month. More than enough for hosting. Now, I'd hazard a guess that most of my numbers are quite a bit on the low side, as reddit has operated for years without CN shutting the doors. Also, from what the admins have intimated from time to time, they make money, but not enough to register on CN's radar.
I wouldn't discount their ad sales; traffic like that carries a lot of weight.