Of course Emily was not made aware of the producer/Arie link until it was beneficial for story line purposes.
The producers know pretty much everything about your life through their vigorous screening process. The skeevy thing about this situation is that Cassie L is Emily's confidante and best friend. Unlike a real best friend, she is by Emily's side almost 24 hours a day. I think she even stayed at Em's house while they were in Charlotte. So she knows who Emily likes/dislikes, insecurities, what she feels about the guys. Then on top of it, Cassie also knows a lot about Arie. In this little bubble she can "prod" Emily towards certain guys and away from others.
They have wanted Arie for a few years now and until now he has always said no. It was now to his benefit to come on this season because Cassie likely knew that Emily would like Arie and that she could get him far (if Emily liked him) and also groom him for the Bachelor if Em didn't choose him. *Jedi mind tricks*
Emily knows how this show works. Of course she was shocked and probably angry to find out that her "other half" dated a man she is currently lusting after. But then rationality kicks in and she is OK with it. This news may dampen her feelings for Arie or it may not, but it makes great television. Emily knows that, and can put it into perspective which is why she can still consider Cassie/Chris/Mike friends. There may be those feelings of how could you do this to me? but they all get over it. As long as people are watching and talking about it, that is what the producers want. It is the outcome and real life that Emily should only be concerned about.
If there is one thing that pissed me off about Emily and Brad's relationship was the fact that she couldn't help but feel jealous of what she saw on TV versus what she actually felt/experienced/lived while dating Brad. She couldn't let that go and it affected their relationship in real life. JP was a smart man and said he only watched his scenes with Ashley. I'd do the same thing, who wants to watch their bf/gf/fiance(e) make out with someone else?