It's known that some applications simply don't work on Bluestacks because of many reasons like outdated operating system, trimmed down version of Android, missing important system files, etc. Bluestacks should be used as a test not for a daily working environment. You'll need an Android phone or tablet for that kind of operation. However, I recommend installing an older version or a rooted version of the Bluestacks App Player. This way chances of getting Uber running are increased.
Download older versions: http://forum.xda-developers.com/wiki/BlueStacks_App_Player