We love build servers (including Jenkins) and have built in support for them right out of the box! You don't need to install or change anything on your build server and your crash reports will be fully symbolicated.
On Android, if you’re using ProGuard just go here: http://support.crashlytics.com/knowledgebase/articles/202140-do-you-support-build-tools-for-android-
Having issues on iOS? Make sure that Xcode.app is closed when building and that Crashlytics.app isn't installed on the build server.
PS: Looking to automate your Beta distributions? Take a look here!