Quicksilver only indexes
/Users/yourusername/Applications/ by default.
In order to have access to Xcode and other Developer Tools simply add a new
File & Folder Scanner from Quicksilver's
Catalog preferences panel and specify
com.apple.application as type. Additionally you need to specify a scan depth of
Once done that, close the Preferences and re-scan your Quicksilver catalog. Then you will be able to launch Xcode the same way you launch other applications.