In case this is useful to anyone else, I've posted an example project showing how to integrate Google Test with an Xcode unit testing bundle:
https://github.com/mattstevens/xcode-googletestIt works by defining an XCTest (or OCUnit) test case that runs Google Test, mapping the output to the format Xcode expects. Test results appear in the build log and Xcode 5's test navigator, and the use of the bundle allows for easy execution against an iOS simulator or device. It also allows you to run both C++ and Objective-C tests in one go if you're working on a library that includes both. I've been using this setup for a few months and so far it's worked out pretty well.
Matt