Something similar happened to me. It's not necessarily that the hire is intended to be sacrificial, but it sometimes falls to the "new guy" to take the hit.
So after about 3-4 months of working at Microsoft, I was ranked in the bottom 10% (the bucket for people who don't have good prospects for furthering their career at Microsoft.) This was back when they used a 10/70/20 system.
Now, don't get me wrong, I don't think I'm some master developer that deserves to always be in the top 20%. I strive to be above average, but I consider myself to be merely average, especially compared to many of the exceptionally bright people working there.
Here's the real bitch. The reason I was given for this rating had nothing to do with my performance. I shit you not, and this is as verbatim as I remember it: "Somebody has to be in the bottom bucket and since you're new, I can't rank you higher."
The problem is that this stuff fucks with your career there. It's a black mark on your record that follows you around. HR assured me that someone being new is not a valid reason to rank someone like that, you have to base it on actual performance.
An easy fix that my previous company had employed: have a "too new to rate" category.
In retrospect, I just had a shitty boss, and it wasn't necessarily reflective of Microsoft as a whole. I also should have challenged it more vigorously, but I didn't want to create animosity between my boss and myself seeing as I was barred from transferring for.. 18 months was it?
I'm not too bitter about it though; I ultimately ended up resigning after a year and then coming back to work for the same department as a contractor at a much higher salary. As such, I no longer had to participate in performance reviews at all.