Well, the thing is, bringing the demons there on purpose makes no *sense* unless they could be sure the angels would be there, too. So, regardless of whether or not Dean knew about the plan when he gave Anna up to Uriel, *Sam* had to have known about the angels coming when he came up with the plan to get the demons there. And Dean clearly wasn't surprised that Ruby brought the demons, so I think he must have known about that part, too. So, what I'm imagining is that Dean gave Anna up because Uriel threatened Sam, but then he went to Sam and told him about it, and together, they agreed on the plan to bring the demons in, as well.

The only problem is that I'm having a *really* hard time imagining Dean going to Sam if he gave Anna up because of Sam without a backup plan. It just... doesn't seem to be in character for Dean to do that. So... I don't know. I'm not sure it completely makes sense, if you really think about it.