We did something very similar. We removed walls and the kitchen is now open to the dining room. Our pulls, faucet and pendants in the kitchen are all satin nickel, but the light above the dining room table has a black stem:

Here's the view from the dining room towards the kitchen:

We also used similar semi-flush lights at either end next to the kitchen, which you can almost see at the very left near the french door:

I was researching this a few days ago as well, and found some articles that said this is not considered wrong from a design standpoint. It sounded like it was more acceptable to mix finishes now, and some people prefer the not so matchy look anyway. I was curious because I have 3 rooms that flow together and I have brushed nickel in two rooms. In the 3rd room I wanted to put in a ORB light. I think it will work fine. I actually just replaced the windows with ORB double curtain rods (and these flow through two rooms).

I also read that if you can add at least a couple pieces in that particular finish it will look even better.... so I felt having the curtain rods and the light would make it work, but I think even without, it's ok. Buy what you love, that is most important!